3,445 research outputs found
Program computes equilibrium normal shock and stagnation point solutions for arbitrary gas mixtures
Program computes solutions for flow parameters in arbitrary gas mixtures behind a normal and a reflected normal shock, for in-flight and shock-tube stagnation conditions. Equilibrium flow calculations are made by a free-energy minimization technique coupled with the steady-flow conservation equations and a modified Newton-Raphson iterative scheme
Lightcone renormalization and quantum quenches in one-dimensional Hubbard models
The Lieb-Robinson bound implies that the unitary time evolution of an
operator can be restricted to an effective light cone for any Hamiltonian with
short-range interactions. Here we present a very efficient renormalization
group algorithm based on this light cone structure to study the time evolution
of prepared initial states in the thermodynamic limit in one-dimensional
quantum systems. The algorithm does not require translational invariance and
allows for an easy implementation of local conservation laws. We use the
algorithm to investigate the relaxation dynamics of double occupancies in
fermionic Hubbard models as well as a possible thermalization. For the
integrable Hubbard model we find a pure power-law decay of the number of doubly
occupied sites towards the value in the long-time limit while the decay becomes
exponential when adding a nearest neighbor interaction. In accordance with the
eigenstate thermalization hypothesis, the long-time limit is reasonably well
described by a thermal average. We point out though that such a description
naturally requires the use of negative temperatures. Finally, we study a
doublon impurity in a N\'eel background and find that the excess charge and
spin spread at different velocities, providing an example of spin-charge
separation in a highly excited state.Comment: published versio
A method for computing chemical-equilibrium compositions of reacting-gas mixtures by reduction to a single iteration equation
Computing equilibrium chemical composition and thermodynamic properties of reacting gas mixtures by reduction to single iterative equatio
Tunneling spectroscopy for probing orbital anisotropy in iron pnictides
Using realistic multi-orbital tight-binding Hamiltonians and the T-matrix
formalism, we explore the effects of a non-magnetic impurity on the local
density of states in Fe-based compounds. We show that scanning tunneling
spectroscopy (STS) has very specific anisotropic signatures that track the
evolution of orbital splitting (OS) and antiferromagnetic gaps. Both
anisotropies exhibit two patterns that split in energy with decreasing
temperature, but for OS these two patterns map onto each other under 90 degree
rotation. STS experiments that observe these signatures should expose the
underlying magnetic and orbital order as a function of temperature across
various phase transitions.Comment: 12 pages, 9 figures, replacement with minor changes suggested by
referee
DWBA analysis of the 13C(6Li,d)17O reaction at 10 MeV/nucleon and its astrophysical implications
The value of the alpha spectroscopic factor (S_alpha) of the 6.356 MeV 1/2+
state of 17O is believed to have significant astrophysical implications due to
the importance of the 13C(alpha,n)16O reaction as a possible source of neutron
production for the s process. To further study this effect, an accurate
measurement of the 13C(6Li,d)17O reaction at E_lab = 60 MeV has been performed
recently by Kubono et al., who found a new value for the spectroscopic factor
of the 6.356 MeV 1/2+ state of 17O based on a distorted wave Born approximation
(DWBA) analysis of these data. This new value, S_alpha approximately = 0.011,
is surprisingly much smaller than those used previously in astrophysical
calculations (S_alpha approximately = 0.3-0.7) and thus poses a serious
question as to the role of the 13C(alpha,n)16O reaction as a source of neutron
production. In this work we perform a detailed analysis of the same
13C(6Li,d)17O data within the DWBA as well as the coupled reaction channel
(CRC) formalism. Our analysis yields an S_alpha value of over an order of
magnitude larger than that of Kubono et al. for the 6.356 MeV 1/2+ state of
17O.Comment: 17 pages, 4 figures, minor changes, accepted by Nuclear Physics
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