245 research outputs found
An Analytical 3D Shape-Based Algorithm Based on Orbits Interpolation for Multi-Revolutions Low-Thrust Trajectory Optimization with Eclipses And Perturbations
A novel 3-dimensional shape based algorithm is proposed in order to extend the domain of analytical solutions to planeto-centric mission scenarios, in which hundreds or thousands of revolutions are required. Due to the strong physical meaning of the shape the method outputs a trajectory close to the real optimal solution. Practical mission constraints are easily formalized, such as maximum thrust threshold and eclipses; moreover, relevant perturbations effects can be considered; free and fixed time of flight are manageable as well. The approach is almost completely analytic, beneficial to significantly lower the computational load, well suited for complex mission scenarios near optimal solutions fast detection
Theoretical analysis of the transmission phase shift of a quantum dot in the presence of Kondo correlations
We study the effects of Kondo correlations on the transmission phase shift of
a quantum dot coupled to two leads in comparison with the experimental
determinations made by Aharonov-Bohm (AB) quantum interferometry. We propose
here a theoretical interpretation of these results based on scattering theory
combined with Bethe ansatz calculations. We show that there is a factor of 2
difference between the phase of the S-matrix responsible for the shift in the
AB oscillations, and the one controlling the conductance. Quantitative
agreement is obtained with experimental results for two different values of the
coupling to the leads.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
Finite temperature strong-coupling expansions for the Kondo lattice model
Strong-coupling expansions, to order , are derived for the Kondo
lattice model of strongly correlated electrons, in 1-, 2- and 3- dimensions at
arbitrary temperature. Results are presented for the specific heat, and spin
and charge susceptibilities.Comment: revtex
Quantum Criticality in doped CePd_1-xRh_x Ferromagnet
CePd_1-xRh_x alloys exhibit a continuous evolution from ferromagnetism (T_C=
6.5 K) at x = 0 to a mixed valence (MV) state at x = 1. We have performed a
detailed investigation on the suppression of the ferromagnetic (F) phase in
this alloy using dc-(\chi_dc) and ac-susceptibility (\chi_ac), specific heat
(C_m), resistivity (\rho) and thermal expansion (\beta) techniques. Our results
show a continuous decrease of T_C (x) with negative curvature down to T_C = 3K
at x*= 0.65, where a positive curvature takes over. Beyond x*, a cusp in cac is
traced down to T_C* = 25 mK at x = 0.87, locating the critical concentration
between x = 0.87 and 0.90. The quantum criticality of this region is recognized
by the -log(T/T_0) dependence of C_m/T, which transforms into a T^-q (~0.5) one
at x = 0.87. At high temperature, this system shows the onset of valence
instability revealed by a deviation from Vegard's law (at x_V~0.75) and
increasing hybridization effects on high temperature \chi_dc and \rho.
Coincidentally, a Fermi liquid contribution to the specific heat arises from
the MV component, which becomes dominant at the CeRh limit. In contrast to
antiferromagnetic systems, no C_m/T flattening is observed for x > x_cr rather
the mentioned power law divergence, which coincides with a change of sign of
\beta. The coexistence of F and MV components and the sudden changes in the T
dependencies are discussed in the context of randomly distributed magnetic and
Kondo couplings.Comment: 11 pages, 11 figure
Similarities between the Hubbard and Periodic Anderson Models at Finite Temperatures
The single band Hubbard and the two band Periodic Anderson Hamiltonians have
traditionally been applied to rather different physical problems - the Mott
transition and itinerant magnetism, and Kondo singlet formation and scattering
off localized magnetic states, respectively. In this paper, we compare the
magnetic and charge correlations, and spectral functions, of the two systems.
We show quantitatively that they exhibit remarkably similar behavior, including
a nearly identical topology of the finite temperature phase diagrams at
half-filling. We address potential implications of this for theories of the
rare earth ``volume collapse'' transition.Comment: 4 pages (RevTeX) including 4 figures in 7 eps files; as to appear in
Phys. Rev. Let
Platinum-free photoelectrochromic devices working with copper-based electrolytes for ultrastable smart windows
Photoelectrochromic systems are devices designed for large-scale manufacturing of smart windows, capable of changing their transmittance according to external environmental conditions. This communication proposes the replacement of the two most critical photoelectrochemical device components studied so far, namely the counter electrode and the redox mediator. Regarding the first, graphene nanoplatelets are used to replace platinum, maintaining both its optical and electrocatalytic properties, and at the same time reducing the device cost. Secondly, a copper-based redox pair was chosen to solve the corrosion problems typically encountered with the iodine-based mediator. The combination of the above components led to devices with high performance (coloration speeds in the order of seconds, with a maximum contrast ratio of 10.4 : 1), as well as the achievement of a long-term stability record (over 400 days) for these photoelectrochromic systems
Self-consistency over the charge-density in dynamical mean-field theory: a linear muffin-tin implementation and some physical implications
We present a simple implementation of the dynamical mean-field theory
approach to the electronic structure of strongly correlated materials. This
implementation achieves full self-consistency over the charge density, taking
into account correlation-induced changes to the total charge density and
effective Kohn-Sham Hamiltonian. A linear muffin-tin orbital basis-set is used,
and the charge density is computed from moments of the many body
momentum-distribution matrix. The calculation of the total energy is also
considered, with a proper treatment of high-frequency tails of the Green's
function and self-energy. The method is illustrated on two materials with
well-localized 4f electrons, insulating cerium sesquioxide Ce2O3 and the
gamma-phase of metallic cerium, using the Hubbard-I approximation to the
dynamical mean-field self-energy. The momentum-integrated spectral function and
momentum-resolved dispersion of the Hubbard bands are calculated, as well as
the volume-dependence of the total energy. We show that full self-consistency
over the charge density, taking into account its modification by strong
correlations, can be important for the computation of both thermodynamical and
spectral properties, particularly in the case of the oxide material.Comment: 20 pages, 6 figures (submitted in The Physical Review B
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