8,950 research outputs found
Anisotropic valence-->core x-ray fluorescence from a [Rh(en)3][Mn(N)(CN)5]·H2O single crystal: Experimental results and density functional calculations
High resolution x-ray fluorescence spectra have been recorded for emission in different directions from a single crystal of the compound [Rh(en)3][Mn(N)(CN)5]·H2O. The spectra are interpreted by comparison with density functional theory (DFT) electronic structure calculations. The Kbeta[double-prime] line, which is strongly polarized along the Mn–N axis, can be viewed as an N(2s)-->Mn(1s) transition, and the angular dependence is understood within the dipole approximation. The so-called Kbeta2,5 region has numerous contributions but is dominated by Mn(4p) and C(2s)-->Mn(1s) transitions. Transition energy splittings are found in agreement with those of calculated occupied molecular orbitals to within 1 eV. Computed relative transition probabilities reproduce experimentally observed trends
The issue of time in generally covariant theories and the Komar-Bergmann approach to observables in general relativity
Diffeomorphism-induced symmetry transformations and time evolution are
distinct operations in generally covariant theories formulated in phase space.
Time is not frozen. Diffeomorphism invariants are consequently not necessarily
constants of the motion. Time-dependent invariants arise through the choice of
an intrinsic time, or equivalently through the imposition of time-dependent
gauge fixation conditions. One example of such a time-dependent gauge fixing is
the Komar-Bergmann use of Weyl curvature scalars in general relativity. An
analogous gauge fixing is also imposed for the relativistic free particle and
the resulting complete set time-dependent invariants for this exactly solvable
model are displayed. In contrast with the free particle case, we show that
gauge invariants that are simultaneously constants of motion cannot exist in
general relativity. They vary with intrinsic time
Lagrangian approach to a symplectic formalism for singular systems
We develop a Lagrangian approach for constructing a symplectic structure for
singular systems. It gives a simple and unified framework for understanding the
origin of the pathologies that appear in the Dirac-Bergmann formalism, and
offers a more general approach for a symplectic formalism, even when there is
no Hamiltonian in a canonical sense. We can thus overcome the usual limitations
of the canonical quantization, and perform an algebraically consistent
quantization for a more general set of Lagrangian systems.Comment: 30 page
A Compact Approximate Solution to the Friedel-Anderson Impuriy Problem
An approximate groundstate of the Anderson-Friedel impurity problem is
presented in a very compact form. It requires solely the optimization of two
localized electron states and consists of four Slater states (Slater
determinants). The resulting singlet ground state energy lies far below the
Anderson mean field solution and agrees well with the numerical results by
Gunnarsson and Schoenhammer, who used an extensive 1/N_{f}-expansion for a spin
1/2 impurity with double occupancy of the impurity level.
PACS: 85.20.Hr, 72.15.R
Oscillations of the magnetic polarization in a Kondo impurity at finite magnetic fields
The electronic properties of a Kondo impurity are investigated in a magnetic
field using linear response theory. The distribution of electrical charge and
magnetic polarization are calculated in real space. The (small) magnetic field
does not change the charge distribution. However, it unmasks the Kondo cloud.
The (equal) weight of the d-electron components with their magnetic moment up
and down is shifted and the compensating s-electron clouds don't cancel any
longer (a requirement for an experimental detection of the Kondo cloud). In
addition to the net magnetic polarization of the conduction electrons an
oscillating magnetic polarization with a period of half the Fermi wave length
is observed. However, this oscillating magnetic polarization does not show the
long range behavior of Rudermann-Kittel-Kasuya-Yosida oscillations because the
oscillations don't extend beyond the Kondo radius. They represent an internal
electronic structure of the Kondo impurity in a magnetic field. PACS: 75.20.Hr,
71.23.An, 71.27.+
Numerical Calculation of the Fidelity for the Kondo and the Friedel-Anderson Impurities
The fidelities of the Kondo and the Friedel-Anderson (FA) impurities are
calculated numerically. The ground states of both systems are calculated with
the FAIR (Friedel artificially inserted resonance) theory. The ground state in
the interacting systems is compared with a nullstate in which the interaction
is zero. The different multi-electron states are expressed in terms of Wilson
states. The use of N Wilson states simulates the use of a large effective
number N_{eff} of states. A plot of ln(F) versus N\proptoln(N_{eff}) reveals
whether one has an Anderson orthogonality catastrophe at zero energy. The
results are at first glance surprising. The ln(F)-ln(N_{eff}) plot for the
Kondo impurity diverges for large N_{eff}. On the other hand, the corresponding
plot for the symmetric FA impurity saturates for large N_{eff} when the level
spacing at the Fermi level is of the order of the singlet-triplet excitation
energy. The behavior of the fidelity allows one to determine the phase shift of
the electron states in this regime. PACS: 75.20.Hr, 71.23.An, 71.27.+a,
05.30.-
Gossip on Weighted Networks
We investigate how suitable a weighted network is for gossip spreading. The
proposed model is based on the gossip spreading model introduced by Lind et.al.
on unweighted networks. Weight represents "friendship." Potential spreader
prefers not to spread if the victim of gossip is a "close friend". Gossip
spreading is related to the triangles and cascades of triangles. It gives more
insight about the structure of a network.
We analyze gossip spreading on real weighted networks of human interactions.
6 co-occurrence and 7 social pattern networks are investigated. Gossip
propagation is found to be a good parameter to distinguish co-occurrence and
social pattern networks. As a comparison some miscellaneous networks and
computer generated networks based on ER, BA, WS models are also investigated.
They are found to be quite different than the human interaction networks.Comment: 8 pages, 4 figures, 1 tabl
- …