34 research outputs found
On the Mechanism of Time--Delayed Feedback Control
The Pyragas method for controlling chaos is investigated in detail from the
experimental as well as theoretical point of view. We show by an analytical
stability analysis that the revolution around an unstable periodic orbit
governs the success of the control scheme. Our predictions concerning the
transient behaviour of the control signal are confirmed by numerical
simulations and an electronic circuit experiment.Comment: 4 pages, REVTeX, 4 eps-figures included Phys. Rev. Lett., in press
also available at
http://athene.fkp.physik.th-darmstadt.de/public/wolfram.htm
Recommended from our members
Demonstartion of density dependence of x-ray flux in a laser-driven hohlraum
Experiments have been conducted using laser-driven cylindrical hohlraums whose walls are machined from Ta{sub 2}O{sub 5} foams of 100 mg/cc and 4 g/cc densities. Measurements of the radiation temperature demonstrate that the lower density walls produce higher radiation temperatures than the high density walls. This is the first experimental demonstration of the prediction that this would occur [M. D. Rosen and J. H. Hammer, Phys. Rev. E 72, 056403 (2005)]. For high density walls, the radiation front propagates subsonically, and part of the absorbed energy is wasted by the flow kinetic energy. For the lower wall density, the front velocity is supersonic and can devote almost all of the absorbed energy to heating the wall
Presence of Amorphous Carbon Nanoparticles in Food Caramels
We report the finding of the presence of carbon nanoparticles (CNPs) in different carbohydrate based food caramels, viz. bread, jaggery, sugar caramel, corn flakes and biscuits, where the preparation involves heating of the starting material. The CNPs were amorphous in nature; the particles were spherical having sizes in the range of 4–30 nm, depending upon the source of extraction. The results also indicated that particles formed at higher temperature were smaller than those formed at lower temperature. Excitation tuneable photoluminescence was observed for all the samples with quantum yield (QY) 1.2, 0.55 and 0.63%, for CNPs from bread, jaggery and sugar caramels respectively. The present discovery suggests potential usefulness of CNPs for various biological applications, as the sources of extraction are regular food items, some of which have been consumed by humans for centuries, and thus they can be considered as safe
Dispersing Individual Single-Wall Carbon Nanotubes in Aqueous Surfactant Solutions below the cmc
Nonperturbing measurements of spatially distributed underwater acoustic fields using a scanning laser Doppler vibrometer
This article was published in the journal, Journal of the Acoustical Society of America [© Acoustical Society of America] and is also available at: http://asa.aip.org/jasa.htmlLocalized changes in the density of water induced by the presence of an acoustic field cause
perturbations in the localized refractive index. This relationship has given rise to a number of
nonperturbing optical metrology techniques for recording measurement parameters from underwater
acoustic fields. A method that has been recently developed involves the use of a Laser Doppler
Vibrometer (LDV) targeted at a fixed, nonvibrating, plate through an underwater acoustic field.
Measurements of the rate of change of optical pathlength along a line section enable the
identification of the temporal and frequency characteristics of the acoustic wave front. This
approach has been extended through the use of a scanning LDV, which facilitates the measurement
of a range of spatially distributed parameters. A mathematical model is presented that relates the
distribution of pressure amplitude and phase in a planar wave front with the rate of change of optical
pathlength measured by the LDV along a specifically orientated laser line section. Measurements of
a 1 MHz acoustic tone burst generated by a focused transducer are described and the results
presented. Graphical depictions of the acoustic power and phase distribution recorded by the LDV
are shown, together with images representing time history during the acoustic wave propagation
Recommended from our members
Thermal decomposition of polystyrene in the high temperature fabrication technology of hollow microspheres. Revision 1
The degree and nature of polymer degradation that occurs in the high temperature microshell formation process developed at the Lebedev Physical Institute has been examined experimentally. We find that significant mass degradation occurs during the final stages of shell formation. This manifests itself both in terms of mass loss and molecular weight degradation as measured by gel permeation chromatography. This decrease in the molecular weight may be in part responsible for the relatively fragile nature of the shells produced by this high temperature process. 9 refs., 6 figs., 2 tabs
Recommended from our members
Vertical movement of soluble carbon and nutrients from biocrusts to subsurface mineral soils
Dryland ecosystems can be constrained by low soil fertility. Within drylands, the soil nutrient and organic carbon (C) cycling that does occur is often mediated by soil surface communities known as biological soil crusts (biocrusts), which cycle C and nutrients in the top ca. 0–2 cm of soil. However, the degree to which biocrusts are influencing soil fertility and biogeochemical cycling in deeper, subsurface mineral soils is unclear. The movement of dissolved resources from biocrusts to deeper soil layers in leachate may be one of the main mechanisms through which biocrust fertility is transferred downward towards deeper microbial communities and plant roots occurring within mineral soil. Here we examined the role of biocrust leachate in contributing to subsurface nutrient and soluble C pools and subsurface microbial cycling. We collected biocrusts from three biocrust successional stages and explored resource pools in situ at multiple soil depths, while collecting leachate and measuring nutrient and organic C concentrations and metabolite composition from each successional stage in the laboratory. After four leachate collections, we conducted an incubation of mineral soil collected from below each biocrust successional stage to measure heterotrophic microbial CO2 flux and biomass. Overall, our findings observed that the degree of nutrient and C connectivity between biocrusts and the sub-crust mineral soil depended on the biocrust successional stage and the element being considered, and the influence of biocrust successional stage on mineral soil CO2 flux is likely related to long-term resource build up. Together, our results suggest that the influence of biocrust leachate on subsurface mineral soil is complex and context dependent, but, over longer time periods and at later successional stages, can have measurable effects on dryland soil biogeochemical cycling with feedbacks to resource availability and CO2 flux