10,893 research outputs found
Excitation of atomic hydrogen to the metasable 2 2S1/2 state by electron impact
Atomic hydrogen excitation to metastable 2 /2/ S sub 1/2 state by electron impac
Polarization of Lyman alpha radiation emitted by H/2S/ atoms in weak electric fields
Polarization prediction in modulated beam of ground state hydrogen atoms crossed by dc electron bea
Rectenna system design
The function of the rectenna in the solar power satellite system is described and the basic design choices based on the desired microwave field concentration and ground clearance requirements are given. One important area of concern, from the EMI point of view, harmonic reradiation and scattering from the rectenna is also designed. An optimization of a rectenna system design to minimize costs was performed. The rectenna cost breakdown for a 56 w installation is given as an example
Impact of strong disorder on the static magnetic properties of the spin-chain compound BaCu2SiGeO7
The disordered quasi-1D magnet BaCu2SiGeO7 is considered as one of the best
physical realizations of the random Heisenberg chain model, which features an
irregular distribution of the exchange parameters and whose ground state is
predicted to be the scarcely investigated random-singlet state (RSS). Based on
extensive 29Si NMR and magnetization studies of BaCu2SiGeO7, combined with
numerical Quantum Monte Carlo simulations, we obtain remarkable quantitative
agreement with theoretical predictions of the random Heisenberg chain model and
strong indications for the formation of a random-singlet state at low
temperatures in this compound. As a local probe, NMR is a well-adapted
technique for studying the magnetism of disordered systems. In this case it
also reveals an additional local transverse staggered field (LTSF), which
affects the low-temperature properties of the RSS. The proposed model
Hamiltonian satisfactorily accounts for the temperature dependence of the NMR
line shapes.Comment: 10 pages, 7 figure
Renormalization of the periodic Anderson model: an alternative analytical approach to heavy Fermion behavior
In this paper a recently developed projector-based renormalization method
(PRM) for many-particle Hamiltonians is applied to the periodic Anderson model
(PAM) with the aim to describe heavy Fermion behavior. In this method
high-energetic excitation operators instead of high energetic states are
eliminated. We arrive at an effective Hamiltonian for a quasi-free system which
consists of two non-interacting heavy-quasiparticle bands. The resulting
renormalization equations for the parameters of the Hamiltonian are valid for
large as well as small degeneracy of the angular momentum. An expansion
in is avoided. Within an additional approximation which adapts the
idea of a fixed renormalized \textit{f} level , we obtain
coupled equations for and the averaged \textit{f}
occupation . These equations resemble to a certain extent those of the
usual slave boson mean-field (SB) treatment. In particular, for large
the results for the PRM and the SB approach agree perfectly whereas
considerable differences are found for small .Comment: 26 pages, 5 figures included, discussion of the DOS added in v2,
accepted for publication in Phys. Rev.
Directed Chaotic Transport in Hamiltonian Ratchets
We present a comprehensive account of directed transport in one-dimensional
Hamiltonian systems with spatial and temporal periodicity. They can be
considered as Hamiltonian ratchets in the sense that ensembles of particles can
show directed ballistic transport in the absence of an average force. We
discuss general conditions for such directed transport, like a mixed classical
phase space, and elucidate a sum rule that relates the contributions of
different phase-space components to transport with each other. We show that
regular ratchet transport can be directed against an external potential
gradient while chaotic ballistic transport is restricted to unbiased systems.
For quantized Hamiltonian ratchets we study transport in terms of the evolution
of wave packets and derive a semiclassical expression for the distribution of
level velocities which encode the quantum transport in the Floquet band
spectra. We discuss the role of dynamical tunneling between transporting
islands and the chaotic sea and the breakdown of transport in quantum ratchets
with broken spatial periodicity.Comment: 22 page
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