1,940 research outputs found
A simple stochastic model for the evolution of protein lengths
We analyse a simple discrete-time stochastic process for the theoretical
modeling of the evolution of protein lengths. At every step of the process a
new protein is produced as a modification of one of the proteins already
existing and its length is assumed to be random variable which depends only on
the length of the originating protein. Thus a Random Recursive Trees (RRT) is
produced over the natural integers. If (quasi) scale invariance is assumed, the
length distribution in a single history tends to a lognormal form with a
specific signature of the deviations from exact gaussianity. Comparison with
the very large SIMAP protein database shows good agreement.Comment: 12 pages, 4 figure
Effect of Quantum Confinement on Electron Tunneling through a Quantum Dot
Employing the Anderson impurity model, we study tunneling properties through
an ideal quantum dot near the conductance minima. Considering the Coulomb
blockade and the quantum confinement on an equal footing, we have obtained
current contributions from various types of tunneling processes; inelastic
cotunneling, elastic cotunneling, and resonant tunneling of thermally activated
electrons. We have found that the inelastic cotunneling is suppressed in the
quantum confinement limit, and thus the conductance near its minima is
determined by the elastic cotunneling at low temperature (,
: dot-reservoir coupling constant), or by the resonant tunneling of
single electrons at high temperature ().Comment: 11 pages Revtex, 2 Postscript figures, To appear in Phys.Rev.
Many Body Effects on Electron Tunneling through Quantum Dots in an Aharonov-Bohm Circuit
Tunneling conductance of an Aharonov-Bohm circuit including two quantum dots
is calculated based on the general expression of the conductance in the linear
response regime of the bias voltage. The calculation is performed in a wide
temperature range by using numerical renormalization group method. Various
types of AB oscillations appear depending on the temperature and the potential
depth of the dots. Especially, AB oscillations have strong higher harmonics
components as a function of the magnetic flux when the potential of the dots is
deep. This is related to the crossover of the spin state due to the Kondo
effect on quantum dots. When the temperature rises up, the amplitude of the AB
oscillations becomes smaller reflecting the breaking of the coherency.Comment: 21 pages, 11 PostScript figures, LaTeX, uses jpsj.sty epsbox.st
Spin-orbit Scattering and the Kondo Effect
The effects of spin-orbit scattering of conduction electrons in the Kondo
regime are investigated theoretically. It is shown that due to time-reversal
symmetry, spin-orbit scattering does not suppress the Kondo effect, even though
it breaks spin-rotational symmetry, in full agreement with experiment. An
orbital magnetic field, which breaks time-reversal symmetry, leads to an
effective Zeeman splitting, which can be probed in transport measurements. It
is shown that, similar to weak-localization, this effect has anomalous magnetic
field and temperature dependence.Comment: 10 pages, RevTex, one postscript figure available on request from
[email protected]
Fine structure in the off-resonance conductance of small Coulomb blockade systems
We show how a fine, multiple-peak structure can arise in the off-resonance,
zero-bias conductance of Coulomb blockade systems. In order to understand how
this effect comes about one must abandon the orthodox, mean-field understanding
of the Coulomb blockade phenomenon and consider quantum fluctuations in the
occupation of the single-particle electronic levels. We illustrate such an
effect with a spinless Anderson-like model for multi-level systems and an
equation-of-motion method for calculating Green's functions that combines two
simple decoupling schemes.Comment: 5 pages, 3 figures, postscript file also available at
http://www.pa.uky.edu/~palacios/papers/eom.ps One figure added. Discussion of
results extende
Transmission Phase Shift of a Quantum Dot with Kondo Correlations
We study the effects of Kondo correlations on the transmission phase shift of
a quantum dot in an Aharonov-Bohm ring. We predict in detail how the
development of a Kondo resonance should affect the dependence of the phase
shift on transport voltage, gate voltage and temperature. This system should
allow the first direct observation of the well-known scattering phase shift of
pi/2 expected (but not directly measurable in bulk systems) at zero temperature
for an electron scattering off a spin-1/2 impurity that is screened into a
singlet.Comment: 4 pages Revtex, 4 figures, final published versio
Excess Kondo resonance in a quantum dot device with normal and superconducting leads: the physics of Andreev-normal co-tunneling
We report on a novel Kondo phenomenon of interacting quantum dots coupled
asymmetrically to a normal and a superconducting lead. The effects of intradot
Coulomb interaction and Andreev tunneling give rise to Andreev bound
resonances. As a result, a new type of co-tunneling process which we term
Andreev-normal co-tunneling, is predicted. At low temperatures, coherent
superposition of these co-tunneling processes induces a Kondo effect in which
Cooper pairs directly participate formation of a spin singlet, leading to four
Kondo resonance peaks in the local density of states, and enhancing the
tunneling current.Comment: 4 pages, 2 figures, Late
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