3 research outputs found
Dielectric relaxation of DNA aqueous solutions
We report on a detailed characterization of complex dielectric response of
Na-DNA aqueous solutions by means of low-frequency dielectric spectroscopy (40
Hz - 110 MHz). Results reveal two broad relaxation modes of strength
20<\Delta\epsilon_LF<100 and 5<\Delta\epsilon_HF<20, centered at 0.5
kHz<\nu_LF<70 kHz and 0.1 MHz<\nu_HF<15 MHz. The characteristic length scale of
the LF process, 50<L_LF<750nm, scales with DNA concentration as
c_DNA^{-0.29\pm0.04} and is independent of the ionic strength in the low added
salt regime. Conversely, the measured length scale of the LF process does not
vary with DNA concentration but depends on the ionic strength of the added salt
as I_s^{-1} in the high added salt regime. On the other hand, the
characteristic length scale of the HF process, 3<L_HF<50 nm, varyes with DNA
concentration as c_DNA^{-0.5} for intermediate and large DNA concentrations. At
low DNA concentrations and in the low added salt limit the characteristic
length scale of the HF process scales as c_DNA^{-0.33}. We put these results in
perspective regarding the integrity of the double stranded form of DNA at low
salt conditions as well as regarding the role of different types of counterions
in different regimes of dielectric dispersion. We argue that the free DNA
counterions are primarily active in the HF relaxation, while the condensed
counterions play a role only in the LF relaxation. We also suggest theoretical
interpretations for all these length scales in the whole regime of DNA and salt
concentrations and discuss their ramifications and limitations.Comment: 15 pages, 9 figure
How to Blend a Robot within a Group of Zebrafish: Achieving Social Acceptance through Real-time Calibration of a Multi-level Behavioural Model
We have previously shown how to socially integrate a fish robot into a group
of zebrafish thanks to biomimetic behavioural models. The models have to be
calibrated on experimental data to present correct behavioural features. This
calibration is essential to enhance the social integration of the robot into
the group. When calibrated, the behavioural model of fish behaviour is
implemented to drive a robot with closed-loop control of social interactions
into a group of zebrafish. This approach can be useful to form mixed-groups,
and study animal individual and collective behaviour by using biomimetic
autonomous robots capable of responding to the animals in long-standing
experiments. Here, we show a methodology for continuous real-time calibration
and refinement of multi-level behavioural model. The real-time calibration, by
an evolutionary algorithm, is based on simulation of the model to correspond to
the observed fish behaviour in real-time. The calibrated model is updated on
the robot and tested during the experiments. This method allows to cope with
changes of dynamics in fish behaviour. Moreover, each fish presents individual
behavioural differences. Thus, each trial is done with naive fish groups that
display behavioural variability. This real-time calibration methodology can
optimise the robot behaviours during the experiments. Our implementation of
this methodology runs on three different computers that perform individual
tracking, data-analysis, multi-objective evolutionary algorithms, simulation of
the fish robot and adaptation of the robot behavioural models, all in
real-time.Comment: 9 pages, 3 figure