203,899 research outputs found
Measuring electron energy distribution by current fluctuations
A recent concept of local noise sensor is extended to measure the energy
resolved electronic energy distribution at a given location
inside a non-equilibrium normal metal interconnect. A quantitative analysis of
is complicated because of a nonlinear differential resistance
of the noise sensor, represented by a diffusive InAs nanowire. Nevertheless, by
comparing the non-equilibrium results with reference equilibrium measurements,
we conclude that is indistinguishable from the Fermi
distribution
Biodiversity, extinctions and evolution of ecosystems with shared resources
We investigate the formation of stable ecological networks where many species
share the same resource. We show that such stable ecosystem naturally occurs as
a result of extinctions. We obtain an analytical relation for the number of
coexisting species and find a relation describing how many species that may go
extinct as a result of a sharp environmental change. We introduce a special
parameter that is a combination of species traits and resource characteristics
used in the model formulation. This parameter describes the pressure on system
to converge, by extinctions. When that stress parameter is large we obtain that
the species traits concentrate at some values. This stress parameter is thereby
a parameter that determines the level of final biodiversity of the system.
Moreover, we show that dynamics of this limit system can be described by simple
differential equations
Transitions between the -core-excited states in Ir, Ir, and Ir ions for clock applications
Iridium ions near - level crossings are the leading candidates for a
new type of atomic clocks with a high projected accuracy and a very high
sensitivity to the temporal variation of the fine structure constant .
To identify spectra of these ions in experiment accurate calculations of the
spectra and electromagnetic transition probabilities should be performed.
Properties of the -core-excited states in Ir, Ir, and
Ir ions are evaluated using relativistic many-body perturbation theory
and Hartree-Fock-Relativistic method (COWAN code). We evaluate excitation
energies, wavelengths, oscillator strengths, and transition rates. Our
large-scale calculations includes the following set of configurations:
with equal to 3, 2, and 1 for the Ir,
Ir, and Ir ions, respectively. The transitions are
illustrated by the synthetic spectra in the 180 - 200 \AA range. Large
contributions of magnetic-dipole transitions to lifetimes of low-lying states
in the region below 2.5 Ry are demonstrated.Comment: 10 page
The Metal-Insulator Transition of the Magneli phase V_4O_7: Implications for V_2O_3
The metal-insulator transition (MIT) of the Magneli phase V_4O_7 is studied
by means of electronic structure calculations using the augmented spherical
wave method. The calculations are based on density functional theory and the
local density approximation. Changes of the electronic structure at the MIT are
discussed in relation to the structural transformations occuring
simultaneously. The analysis is based on a unified point of view of the crystal
structures of all Magneli phase compounds V_nO_2n-1 (3 =< n =< 9) as well as of
VO_2 and V_2O_3. This allows to group the electronic bands into states behaving
similar to the dioxide or the sesquioxide. In addition, the relationship
between the structural and electronic properties near the MIT of these oxides
can be studied on an equal footing. For V_4O_7, a strong influence of
metal-metal bonding across octahedral faces is found for states both parallel
and perpendicular to the hexagonal c_hex axis of V_2O_3. Furthermore, the
structural changes at the MIT cause localization of those states, which mediate
in-plane metal-metal bonding via octahedral edges. This band narrowing opens
the way to an increased influence of electronic correlations, which are
regarded as playing a key role for the MIT of V_2O_3.Comment: 7 pages, 3 figures, more information at
http://www.physik.uni-augsburg.de/~eyert
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