4,735 research outputs found
Electron-hydrogen scattering in Faddeev-Merkuriev integral equation approach
Electron-hydrogen scattering is studied in the Faddeev-Merkuriev integral
equation approach. The equations are solved by using the Coulomb-Sturmian
separable expansion technique. We present - and -wave scattering and
reactions cross sections up to the threshold.Comment: 2 eps figure
Resonant-state solution of the Faddeev-Merkuriev integral equations for three-body systems with Coulomb potentials
A novel method for calculating resonances in three-body Coulombic systems is
proposed. The Faddeev-Merkuriev integral equations are solved by applying the
Coulomb-Sturmian separable expansion method. The S-state
resonances up to threshold are calculated.Comment: 6 pages, 2 ps figure
Jets and produced particles in pp collisions from SPS to RHIC energies for nuclear applications
Higher-order pQCD corrections play an important role in the reproduction of
data at high transverse momenta in the energy range 20 GeV GeV. Recent calculations of photon and pion production in collisions
yield detailed information on the next-to-leading order contributions. However,
the application of these results in proton-nucleus and nucleus-nucleus
collisions is not straightforward. The study of nuclear effects requires a
simplified understanding of the output of these computations. Here we summarize
our analysis of recent calculations, aimed at handling the NLO results by
introducing process and energy-dependent factors.Comment: 4 pages with 5 eps figures include
Continued fraction representation of the Coulomb Green's operator and unified description of bound, resonant and scattering states
If a quantum mechanical Hamiltonian has an infinite symmetric tridiagonal
(Jacobi) matrix form in some discrete Hilbert-space basis representation, then
its Green's operator can be constructed in terms of a continued fraction. As an
illustrative example we discuss the Coulomb Green's operator in
Coulomb-Sturmian basis representation. Based on this representation, a quantum
mechanical approximation method for solving Lippmann-Schwinger integral
equations can be established, which is equally applicable for bound-, resonant-
and scattering-state problems with free and Coulombic asymptotics as well. The
performance of this technique is illustrated with a detailed investigation of a
nuclear potential describing the interaction of two particles.Comment: 7 pages, 4 ps figures, revised versio
Optimization of spatiotemporally fractionated radiotherapy treatments with bounds on the achievable benefit
Spatiotemporal fractionation schemes, that is, treatments delivering
different dose distributions in different fractions, may lower treatment side
effects without compromising tumor control. This is achieved by
hypofractionating parts of the tumor while delivering approximately uniformly
fractionated doses to the healthy tissue. Optimization of such treatments is
based on biologically effective dose (BED), which leads to computationally
challenging nonconvex optimization problems. Current optimization methods yield
only locally optimal plans, and it has been unclear whether these are close to
the global optimum. We present an optimization model to compute rigorous bounds
on the normal tissue BED reduction achievable by such plans.
The approach is demonstrated on liver tumors, where the primary goal is to
reduce mean liver BED without compromising other treatment objectives. First a
uniformly fractionated reference plan is computed using convex optimization.
Then a nonconvex quadratically constrained quadratic programming model is
solved to local optimality to compute a spatiotemporally fractionated plan that
minimizes mean liver BED subject to the constraints that the plan is no worse
than the reference plan with respect to all other planning goals. Finally, we
derive a convex relaxation of the second model in the form of a semidefinite
programming problem, which provides a lower bound on the lowest achievable mean
liver BED.
The method is presented on 5 cases with distinct geometries. The computed
spatiotemporal plans achieve 12-35% mean liver BED reduction over the reference
plans, which corresponds to 79-97% of the gap between the reference mean liver
BEDs and our lower bounds. This indicates that spatiotemporal treatments can
achieve substantial reduction in normal tissue BED, and that local optimization
provides plans that are close to realizing the maximum potential benefit
Effective Q-Q Interactions in Constituent Quark Models
We study the performance of some recent potential models suggested as
effective interactions between constituent quarks. In particular, we address
constituent quark models for baryons with hybrid Q-Q interactions stemming from
one-gluon plus meson exchanges. Upon recalculating two of such models we find
them to fail in describing the N and \Delta spectra. Our calculations are based
on accurate solutions of the three-quark systems in both a variational
Schr\"odinger and a rigorous Faddeev approach. It is argued that hybrid {Q-Q}
interactions encounter difficulties in describing baryon spectra due to the
specific contributions from one-gluon and pion exchanges together. In contrast,
a chiral constituent quark model with a Q-Q interaction solely derived from
Goldstone-boson exchange is capable of providing a unified description of both
the N and \Delta spectra in good agreement with phenomenology.Comment: 21 pages, LaTe
Three-potential formalism for the three-body scattering problem with attractive Coulomb interactions
A three-body scattering process in the presence of Coulomb interaction can be
decomposed formally into a two-body single channel, a two-body multichannel and
a genuine three-body scattering. The corresponding integral equations are
coupled Lippmann-Schwinger and Faddeev-Merkuriev integral equations. We solve
them by applying the Coulomb-Sturmian separable expansion method. We present
elastic scattering and reaction cross sections of the system both below
and above the threshold. We found excellent agreements with previous
calculations in most cases.Comment: 12 pages, 3 figure
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