8,973 research outputs found
Quantum Hall Effect induced by electron-electron interaction in disordered GaAs layers with 3D spectrum
It is shown that the observed Quantum Hall Effect in epitaxial layers of
heavily doped n-type GaAs with thickness (50-140 nm) larger the mean free path
of the conduction electrons (15-30 nm) and, therefore, with a three-dimensional
single-particle spectrum is induced by the electron-electron interaction. The
Hall resistance R_xy of the thinnest sample reveals a wide plateau at small
activation energy E_a=0.4 K found in the temperature dependence of the
transverse resistance R_xx. The different minima in the transverse conductance
G_xx of the different samples show a universal temperature dependence
(logarithmic in a large range of rescaled temperatures T/T_0) which is
reminiscent of electron-electron-interaction effects in coherent diffusive
transport.Comment: 6 pages, 3 figures, 1 tabl
PRED-CLASS: cascading neural networks for generalized protein classification and genome-wide applications
A cascading system of hierarchical, artificial neural networks (named
PRED-CLASS) is presented for the generalized classification of proteins into
four distinct classes-transmembrane, fibrous, globular, and mixed-from
information solely encoded in their amino acid sequences. The architecture of
the individual component networks is kept very simple, reducing the number of
free parameters (network synaptic weights) for faster training, improved
generalization, and the avoidance of data overfitting. Capturing information
from as few as 50 protein sequences spread among the four target classes (6
transmembrane, 10 fibrous, 13 globular, and 17 mixed), PRED-CLASS was able to
obtain 371 correct predictions out of a set of 387 proteins (success rate
approximately 96%) unambiguously assigned into one of the target classes. The
application of PRED-CLASS to several test sets and complete proteomes of
several organisms demonstrates that such a method could serve as a valuable
tool in the annotation of genomic open reading frames with no functional
assignment or as a preliminary step in fold recognition and ab initio structure
prediction methods. Detailed results obtained for various data sets and
completed genomes, along with a web sever running the PRED-CLASS algorithm, can
be accessed over the World Wide Web at http://o2.biol.uoa.gr/PRED-CLAS
One way to Characterize the compact structures of lattice protein model
On the study of protein folding, our understanding about the protein
structures is limited. In this paper we find one way to characterize the
compact structures of lattice protein model. A quantity called Partnum is given
to each compact structure. The Partnum is compared with the concept
Designability of protein structures emerged recently. It is shown that the
highly designable structures have, on average, an atypical number of local
degree of freedom. The statistical property of Partnum and its dependence on
sequence length is also studied.Comment: 10 pages, 5 figure
Hopping conductivity in heavily doped n-type GaAs layers in the quantum Hall effect regime
We investigate the magnetoresistance of epitaxially grown, heavily doped
n-type GaAs layers with thickness (40-50 nm) larger than the electronic mean
free path (23 nm). The temperature dependence of the dissipative resistance
R_{xx} in the quantum Hall effect regime can be well described by a hopping law
(R_{xx} \propto exp{-(T_0/T)^p}) with p=0.6. We discuss this result in terms of
variable range hopping in a Coulomb gap together with a dependence of the
electron localization length on the energy in the gap. The value of the
exponent p>0.5 shows that electron-electron interactions have to be taken into
account in order to explain the occurrence of the quantum Hall effect in these
samples, which have a three-dimensional single electron density of states.Comment: 5 pages, 2 figures, 1 tabl
On the Phase Boundaries of the Integer Quantum Hall Effect. II
It is shown that the statements about the observation of the transitions
between the insulating phase and the integer quantum Hall effect phases with
the quantized Hall conductivity made in a
number of works are unjustified. In these works, the crossing points of the
magnetic field dependences of the diagonal resistivity at different
temperatures at have been misidentified as the
critical points of the phase transitions. In fact, these crossing points are
due to the sign change of the derivative owing to the quantum
corrections to the conductivity.Comment: 3 pages, 2 figure
The effect of the relative nuclear size on the nucleus-nucleus interactions
The experimental data on the interactions of light nuclei (d, He(4), C(12)) at the momentum 4.2 GeV/cA with the carbon nuclei were taken in the 2-m propane bubble chamber. The distributions in the number of interacting nucleons, the spectra of protons, the mean energies of secondary pions and protons, the mean fractions of energy transferred to the pion and nucleon components are presented. The results of the investigation of the mechanism of nucleus-nucleus interactions can be used to calculate the nuclear cascades in the atmosphere
Experimental probes of emergent symmetries in the quantum Hall system
Experiments studying renormalization group flows in the quantum Hall system
provide significant evidence for the existence of an emergent holomorphic
modular symmetry . We briefly review this evidence and show that,
for the lowest temperatures, the experimental determination of the position of
the quantum critical points agrees to the parts \emph{per mille} level with the
prediction from . We present evidence that experiments giving
results that deviate substantially from the symmetry predictions are not cold
enough to be in the quantum critical domain. We show how the modular symmetry
extended by a non-holomorphic particle-hole duality leads to an extensive web
of dualities related to those in plateau-insulator transitions, and we derive a
formula relating dual pairs of magnetic field strengths across any
transition. The experimental data obtained for the transition studied so far is
in excellent agreement with the duality relations following from this emergent
symmetry, and rule out the duality rule derived from the ``law of corresponding
states". Comparing these generalized duality predictions with future
experiments on other transitions should provide stringent tests of modular
duality deep in the non-linear domain far from the quantum critical points.Comment: 12 pages, 9 figure
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