24 research outputs found
Local fluctuations in an aging glass
Polarization fluctuations were measured in nanoscale volumes of a polymer
glass during aging following a temperature quench through the glass transition.
Statistical properties of the noise were studied in equilibrium and during
aging. The noise spectral density had a larger temporal variance during aging,
i.e. the noise was more non-Gaussian, demonstrating stronger correlations
during aging
Observation of Fluctuation-Dissipation-Theorem Violations in a Structural Glass
The fluctuation-dissipation theorem (FDT), connecting dielectric
susceptibility and polarization noise was studied in glycerol below its glass
transition temperature Tg. Weak FDT violations were observed after a quench
from just above to just below Tg, for frequencies above the alpha peak.
Violations persisted up to 10^5 times the thermal equilibration time of the
configurational degrees of freedom under study, but comparable to the average
relaxation time of the material. These results suggest that excess energy flows
from slower to faster relaxing modes.Comment: Improved discussion; final version to appear in Phys. Rev. Lett. 4
pages, 5 PS figures, RevTe
Cascade Boltzmann - Langevin approach to higher-order current correlations in diffusive metal contacts
The Boltzmann - Langevin approach is extended to calculations of third and
fourth cumulants of current in diffusive-metal contacts. These cumulants result
from indirect correlations between current fluctuations, which may be
considered as "noise of noise". The calculated third cumulant coincides exactly
with its quantum-mechanical value. The fourth cumulant tends to its
quantum-mechanical value at high voltages and to a positive value
at V=0 changing its sign at .Comment: 6 pages, 2 eps figures, typo corrected, minor change
Remanence effects in the electrical resistivity of spin glasses
We have measured the low temperature electrical resistivity of Ag : Mn
mesoscopic spin glasses prepared by ion implantation with a concentration of
700 ppm. As expected, we observe a clear maximum in the resistivity (T ) at a
temperature in good agreement with theoretical predictions. Moreover, we
observe remanence effects at very weak magnetic fields for the resistivity
below the freezing temperature Tsg: upon Field Cooling (fc), we observe clear
deviations of (T ) as compared with the Zero Field Cooling (zfc); such
deviations appear even for very small magnetic fields, typically in the Gauss
range. This onset of remanence for very weak magnetic fields is reminiscent of
the typical signature on magnetic susceptibility measurements of the spin glass
transition for this generic glassy system
Noise Probe of the Dynamic Phase Separation in La2/3Ca1/3MnO3
Giant Random Telegraph Noise (RTN) in the resistance fluctuation of a
macroscopic film of perovskite-type manganese oxide La2/3Ca1/3MnO3 has been
observed at various temperatures ranging from 4K to 170K, well below the Curie
temperature (TC = 210K). The amplitudes of the two-level-fluctuations (TLF)
vary from 0.01% to 0.2%. We use a statistical analysis of the life-times of the
TLF to gain insight into the microscopic electronic and magnetic state of this
manganite. At low temperature (below 30K) The TLF is well described by a
thermally activated two-level model. An estimate of the energy difference
between the two states is inferred. At higher temperature (between 60K and
170K) we observed critical effects of the temperature on the life-times of the
TLF. We discuss this peculiar temperature dependence in terms of a sharp change
in the free energy functional of the fluctuators. We attribute the origin of
the RTN to be a dynamic mixed-phase percolative conduction process, where
manganese clusters switch back and forth between two phases that differ in
their conductivity and magnetization.Comment: 15 pages, PDF only, Phys. Rev. Lett. (in press
Universality and Shannon entropy of codon usage
The distribution functions of the codon usage probabilities, computed over
all the available GenBank data, for 40 eukaryotic biological species and 5
chloroplasts, do not follow a Zipf law, but are best fitted by the sum of a
constant, an exponential and a linear function in the rank of usage. For
mitochondriae the analysis is not conclusive. A quantum-mechanics-inspired
model is proposed to describe the observed behaviour. These functions are
characterized by parameters that strongly depend on the total GC content of the
coding regions of biological species. It is predicted that the codon usage is
the same in all exonic genes with the same GC content. The Shannon entropy for
codons, also strongly depending on the exonic GC content, is computed.Comment: Latex 25 pages, 21 figure