1,099 research outputs found
On unbalanced Boolean functions with best correlation immunity
It is known that the order of correlation immunity of a nonconstant
unbalanced Boolean function in variables cannot exceed ; moreover,
it is if and only if the function corresponds to an equitable
-partition of the -cube with an eigenvalue of the quotient matrix.
The known series of such functions have proportion , , or of
the number of ones and zeros. We prove that if a nonconstant unbalanced Boolean
function attains the correlation-immunity bound and has ratio of the
number of ones and zeros, then is divisible by . In particular, this
proves the nonexistence of equitable partitions for an infinite series of
putative quotient matrices. We also establish that there are exactly
equivalence classes of the equitable partitions of the -cube with quotient
matrix and classes, with . These
parameters correspond to the Boolean functions in variables with
correlation immunity and proportion and , respectively (the case
remains unsolved). This also implies the characterization of the
orthogonal arrays OA and OA.Comment: v3: final; title changed; revised; OA(512,11,2,6) discusse
Evidence of the virtual Anderson transition in a narrow impurity band of p-GaAs/AlGaAs quantum wells: conductivity and electric breakdown at low temperatures
In highly doped uncompensated p-type layers within the central part of
GaAs/AlGaAs quantum wells at low temperatures we observed an activated behavior
of the conductivity with low activation energies (1-3) meV which can not be
ascribed to standard mechanisms. We attribute this behavior to the
delocalization of hole states near the maximum of the narrow impurity band in
the sense of the Anderson transition. Low temperature conduction
is supported by an activation of minority carriers - electrons (resulting from
a weak compensation by back-ground defects) - from the Fermi level to the band
of delocalized states mentioned above. The corresponding behavior can be
specified as virtual Anderson transition. Low temperature transport ( K)
exhibits also strong nonlinearity of a breakdown type characterized in
particular by S-shaped I-V curve. The nonlinearity is observed in unexpectedly
low fields ( V/cm). Such a behavior can be explained by a simple model
implying an impact ionization of the localized states of the minority carriers
mentioned above to the band of Anderson-delocalized states.Comment: 9 pages, 6 fi
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