14 research outputs found
Inconsistencies between chemistry–climate models and observed lower stratospheric ozone trends since 1998
No full textThe stratospheric ozone layer shields surface life from harmful ultraviolet radiation. Following the Montreal Protocol ban on long-lived ozone-depleting substances (ODSs), rapid depletion of total column ozone (TCO) ceased in the late 1990s, and ozone above 32 km is now clearly recovering. However, there is still no confirmation of TCO recovery, and evidence has emerged that ongoing quasi-global (60∘ S–60∘ N) lower stratospheric ozone decreases may be responsible, dominated by low latitudes (30∘ S–30∘ N). Chemistry–climate models (CCMs) used to project future changes predict that lower stratospheric ozone will decrease in the tropics by 2100 but not at mid-latitudes (30–60∘). Here, we show that CCMs display an ozone decline similar to that observed in the tropics over 1998–2016, likely driven by an increase in tropical upwelling. On the other hand, mid-latitude lower stratospheric ozone is observed to decrease, while CCMs that specify real-world historical meteorological fields instead show an increase up to present day. However, these cannot be used to simulate future changes; we demonstrate here that free-running CCMs used for projections also show increases. Despite opposing lower stratospheric ozone changes, which should induce opposite temperature trends, CCMs and observed temperature trends agree; we demonstrate that opposing model–observation stratospheric water vapour (SWV) trends, and their associated radiative effects, explain why temperature changes agree in spite of opposing ozone trends. We provide new evidence that the observed mid-latitude trends can be explained by enhanced mixing between the tropics and extratropics. We further show that the temperature trends are consistent with the observed mid-latitude ozone decrease. Together, our results suggest that large-scale circulation changes expected in the future from increased greenhouse gases (GHGs) may now already be underway but that most CCMs do not simulate mid-latitude ozone layer changes well. However, it is important to emphasise that the periods considered here are short, and internal variability that is both intrinsic to each CCM and different to observed historical variability is not well-characterised and can influence trend estimates. Nevertheless, the reason CCMs do not exhibit the observed changes needs to be identified to allow models to be improved in order to build confidence in future projections of the ozone layer.Atmospheric Remote Sensin
Controlling chaos may induce new attractors in an optical device
No full textThe logistic map has been used to describe period doubling bifurcations for periodically modulated lasers. It also represents an asymptotic approximation of Ikeda's map for a passive ring cavity. Because various control methods have been used recently to stabilize branches of periodic solutions in lasers, we investigate the logistic map with a standard Ott, Grebogi and Yorke (OGY) control. We explore the structure of this map plus perturbations and find considerable modifications to its bifurcation diagram. In addition to the original fixed points, we find a new fixed point and new period doubling bifurcations. We show that for certain values of small perturbations the new fixed point of the perturbed logistic map is stable, while its original fixed point becomes unstable. Our analysis suggests that new branches of solutions may exist in lasers as a result of the feedback control. © 1995.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
A, B, C of three-qubit entanglement: three vectors to control it all
No full textIn this paper we are focusing on entanglement control problem in a three-qubit system. We demonstrate that vector representation of entanglement, associated with SO(6) representation of SU(4) two-qubit group, can be used to solve various control problems analytically including (i) the transformation between a W- type states and GHZ state, and (ii) manipulating bipartite concurrences and three-tangle under a restricted access to only two qubits, and (iii) designing USp(4)- type quaternionic operations and quantum states.The presentation of the authors' names and (or) special characters in the title of the pdf file of the accepted manuscript may differ slightly from what is displayed on the item page. The information in the pdf file of the accepted manuscript reflects the original submission by the author
Mechanism for period-doubling bifurcation in a semiconductor laser subject to optical injection
No full textThe single-mode rate equations for a semiconductor laser subject to optical injection are investigated analytically. We determine the first branch of periodic solutions for low values of the injection field. For larger values of the injection field, we derive a third-order pendulum equation for the phase difference of the laser field of the form ψ‴+ψ′=Λ cos(ψ), where Λ groups all the key laser parameters. This equation captures several aspects of the numerical bifurcation diagram, namely, the fixed amplitude of the period-one solution and the period-doubling bifurcation. Finally, we compute the optical power spectrum utilizing the perturbation solutions of the phase equation before and after the period-doubling transition. We also obtain very good agreement with the numerically computed spectrum.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Lang and Kobayashi phase equation
No full textLang and Kobayashi equations for a semiconductor laser subject to optical feedback are investigated by using asymptotic methods. Our analysis is based on the values of two key parameters, namely, the small ratio of the photon and carrier lifetimes and the relatively large value of the linewidth enhancement factor. For low feedback levels, we derive a third-order delay-differential equation for the phase of the laser field. We then show analytically and numerically that this equation admits coexisting branches of stable periodic solutions that appear at different and almost constant amplitudes. These amplitudes are proportional to the roots of the Bessel function J1(x). The bifurcation diagram of the phase equation is in good agreement with the numerical bifurcation diagram of the original Lang and Kobayashi equations. We interpret the onset of the periodic solutions as the emergence of a new set of external cavity modes with a more complicated time dependence.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
