8,003 research outputs found
Dynamics of Turing patterns under spatio-temporal forcing
We study, both theoretically and experimentally, the dynamical response of
Turing patterns to a spatio-temporal forcing in the form of a travelling wave
modulation of a control parameter. We show that from strictly spatial
resonance, it is possible to induce new, generic dynamical behaviors, including
temporally-modulated travelling waves and localized travelling soliton-like
solutions. The latter make contact with the soliton solutions of P. Coullet
Phys. Rev. Lett. {\bf 56}, 724 (1986) and provide a general framework which
includes them. The stability diagram for the different propagating modes in the
Lengyel-Epstein model is determined numerically. Direct observations of the
predicted solutions in experiments carried out with light modulations in the
photosensitive CDIMA reaction are also reported.Comment: 6 pages, 5 figure
N=1 gauge superpotentials from supergravity
We review the supergravity derivation of some non-perturbatively generated
effective superpotentials for N=1 gauge theories. Specifically, we derive the
Veneziano-Yankielowicz superpotential for pure N=1 Super Yang-Mills theory from
the warped deformed conifold solution, and the Affleck-Dine-Seiberg
superpotential for N=1 SQCD from a solution describing fractional D3-branes on
a C^3 / Z_2 x Z_2 orbifold.Comment: LaTeX, iopart class, 8 pages, 3 figures. Contribution to the
proceedings of the workshop of the RTN Network "The quantum structure of
space-time and the geometric nature of fundamental interactions", Copenhagen,
September 2003; v2: published version with minor clarification
Dynamical effects induced by long range activation in a nonequilibrium reaction-diffusion system
We both show experimentally and numerically that the time scales separation
introduced by long range activation can induce oscillations and excitability in
nonequilibrium reaction-diffusion systems that would otherwise only exhibit
bistability. Namely, we show that the Chlorite-Tetrathionate reaction, where
autocatalytic species diffuses faster than the substrates, the spatial
bistability domain in the nonequilibrium phase diagram is extended with
oscillatory and excitability domains. A simple model and a more realistic model
qualitatively account for the observed behavior. The latter model provides
quantitative agreement with the experiments.Comment: 19 pages + 9 figure
Reaction-Diffusion System in a Vesicle with Semi-Permeable Membrane
We study the Schloegl model in a vesicle with semi-permeable membrane. The
diffusion constant takes a smaller value in the membrane region, which prevents
the outflow of self-catalytic product. A nonequilibrium state is stably
maintained inside of the vesicle. Nutrients are absorbed and waste materials
are exhausted through the membrane by diffusion. It is interpreted as a model
of primitive metabolism in a cell.Comment: 8 pages, 6 figure
Aircraft based four-channel thermal dissociation laser induced fluorescence instrument for simultaneous measurements of NO2, total peroxy nitrate, total alkyl nitrate, and HNO3
A four-channel thermal dissociation laser induced fluorescence (TD-LIF) instrument has been developed for simultaneous measurements of nitrogen dioxide (NO2), total peroxy nitrate (âPNs), total alkyl nitrate (âANs) and nitric acid (HNO3). NO2 is measured directly by LIF at 532 nm, whereas organic nitrates and nitric acid are thermally dissociated at distinct temperatures in the inlet to form NO2, which is then measured by LIF. The concentrations of each dissociated species are derived by the differences in measured NO2 relative to the reference colder inlet channel. The TD-LIF was adapted to fly on board the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe 146-301 atmospheric research aircraft in summer 2010, and to date has successfully flown in five field campaigns. This paper reports novel improvements in the TD-LIF instrumentations, including (1) the use of a single wavelength laser, which makes the system compact and relatively cheap; (2) the use of a single beam laser that allows easy alignment and optical stability against the vibrational aircraft environment; and (3) the optical assembly of four detection cells that allow simultaneous and fast (time resolution up to 0.1 s) measurements of NO2, âPNs, âANs and HNO3. Laboratory-generated mixtures of PNs, ANs and HNO3 in zero air are converted into NO2 and used to fix the dissociation temperatures of each heated inlet to test the selectivity of the instrument and potential interferences due to recombination reactions of the dissociated products. The effectiveness of the TD-LIF was demonstrated during the RONOCO aircraft campaign (summer 2010). A chemiluminescence system that was measuring NO2 and a broadband cavity enhanced absorption spectrometer (BBCEAS) that was measuring one of the PNs (N2O5) were installed on the same aircraft during the campaign. The in-flight intercomparison of the new TD-LIF with the chemiluminescence system for NO2 measurements and the intercomparison between âPNs measured by the TD-LIF and N2O5 by the BBCEAS are used to assess the performance of the TD-LIF
- âŠ