Decoherence and Turbulence Sources in a Long Laser.

We investigate the turn-on process in a laser cavity where the round-trip time is several orders of magnitude greater than the active medium timescales. In this long delay limit, we show that the universal evolution of the photon statistics from thermal to Poissonian distribution involves the emergence of power dropouts. While the largest number of these dropouts vanish after a few round-trips, some of them persist and seed coherent structures similar to dark solitons or Nozaki-Bekki holes described by the complex Ginzburg-Landau equation. These coherent structures connect stationary laser emission domains having different optical frequencies. Moreover, they emit intensity bursts which travel at a different speed, and, depending on the cavity dispersion sign, they may collide with other coherent structures, thus leading to an overall turbulent dynamics. The dynamics is well-modeled by delay differential equations from which we compute the laser coherence time evolution at each round-trip and quantify the decoherence induced by the collisions between coherent structures.

Ecological and conceptual consequences of Arctic pollution.

Although the effect of pollution on forest health and decline received much attention in the 1980s, it has not been considered to explain the 'Divergence Problem' in dendroclimatology; a decoupling of tree growth from rising air temperatures since the 1970s. Here we use physical and biogeochemical measurements of hundreds of living and dead conifers to reconstruct the impact of heavy industrialisation around Norilsk in northern Siberia. Moreover, we develop a forward model with surface irradiance forcing to quantify long-distance effects of anthropogenic emissions on the functioning and productivity of Siberia's taiga. Downwind from the world's most polluted Arctic region, tree mortality rates of up to 100% have destroyed 24,000 km2 boreal forest since the 1960s, coincident with dramatic increases in atmospheric sulphur, copper, and nickel concentrations. In addition to regional ecosystem devastation, we demonstrate how 'Arctic Dimming' can explain the circumpolar 'Divergence Problem', and discuss implications on the terrestrial carbon cycle.

Turbulent coherent structures in a long cavity semiconductor laser near the lasing threshold.

We report on the formation of novel turbulent coherent structures in a long cavity semiconductor laser near the lasing threshold. Experimentally, the laser emits a series of power dropouts within a roundtrip, and the number of dropouts per series depends on a set of parameters including the bias current. At fixed parameters, the drops remain dynamically stable, repeating over many roundtrips. By reconstructing the laser electric field in the case where the laser emits one dropout per roundtrip and simulating its dynamics using a time-delayed model, we discuss the reasons for long-term sustainability of these solutions. We suggest that the observed dropouts are closely related to the coherent structures of the cubic complex Ginzburg-Landau equation.

Turbulent coherent structures in a long cavity semiconductor laser near the lasing threshold: publisher's note.

This publisher's note contains corrections to Opt. Lett.45, 4903 (2020)OPLEDP0146-959210.1364/OL.397840.

Dispersive Time-Delay Dynamical Systems.

We present a theoretical approach to investigate the effect of dispersion in dynamical systems commonly described by time-delay models. The introduction of a polarization equation provides a means to introduce dispersion as a distributed delay term. The expansion of this term in power series, as usually performed to study the propagation of waves in spatially extended systems, can lead to the appearance of spurious instabilities. This approach is illustrated using a long cavity laser, where in the normal dispersion regime both the experiment and theory show a stable operation, while a modulation instability, commonly referred as the Benjamin-Feir instability, is observed in the anomalous dispersion regime.

Memory and adaptive behavior in population dynamics: anti-predator behavior as a case study.

Memory allows organisms to forecast the future on the basis of experience, and thus, in some form, is important for the development of flexible adaptive behavior by animal communities. To model memory, we use the concept of hysteresis, which mathematically is described by the Preisach operator. As a case study, we consider anti-predator adaptation in the classic Lotka-Volterra predator-prey model. Despite its simplicity, the model allows us to naturally incorporate essential features of an adaptive system and memory. Our analysis and simulations show that a system with memory can have a continuum of equilibrium states with non-trivial stability properties. The main factor that determines the actual equilibrium state to which a trajectory converges is the maximal number achieved by the population of predator along this trajectory.

Adaptive behaviour and multiple equilibrium states in a predator-prey model.

There is evidence that multiple stable equilibrium states are possible in real-life ecological systems. Phenomenological mathematical models which exhibit such properties can be constructed rather straightforwardly. For instance, for a predator-prey system this result can be achieved through the use of non-monotonic functional response for the predator. However, while formal formulation of such a model is not a problem, the biological justification for such functional responses and models is usually inconclusive. In this note, we explore a conjecture that a multitude of equilibrium states can be caused by an adaptation of animal behaviour to changes of environmental conditions. In order to verify this hypothesis, we consider a simple predator-prey model, which is a straightforward extension of the classic Lotka-Volterra predator-prey model. In this model, we made an intuitively transparent assumption that the prey can change a mode of behaviour in response to the pressure of predation, choosing either "safe" of "risky" (or "business as usual") behaviour. In order to avoid a situation where one of the modes gives an absolute advantage, we introduce the concept of the "cost of a policy" into the model. A simple conceptual two-dimensional predator-prey model, which is minimal with this property, and is not relying on odd functional responses, higher dimensionality or behaviour change for the predator, exhibits two stable co-existing equilibrium states with basins of attraction separated by a separatrix of a saddle point.

Bistable regimes in an optically injected mode-locked laser.

We study experimentally the dynamics of quantum-dot (QD) passively mode-locked semiconductor lasers under external optical injection. The lasers demonstrated multiple dynamical states, with bifurcation boundaries that depended upon the sign of detuning variation. The area of the hysteresis loops grew monotonically at small powers of optical injection and saturated at moderate powers. At high injection levels the hysteresis decreased and eventually disappeared.

alpha-tubulin minichromosome promoters in the stichotrichous ciliate Stylonychia lemnae.

Ciliated protists are model organisms for a number of molecular phenomena including telomerase function, self-splicing introns, and an RNA interference-related mechanism in programmed DNA elimination. Despite this relevance, our knowledge about promoters and transcriptional regulation in these organisms is very limited. The macronuclear genome of stichotrichous ciliates consists of minichromosomes which typically encode a single gene. The 5' nontranscribed spacers are usually no longer than 400 bp and highly suitable for promoter characterizations. We used microinjection of two artificial and differently tagged alpha1 tubulin minichromosomes into the macronucleus of Stylonychia lemnae as a means to characterize in detail the corresponding promoter. Clonal cell lines that stably maintained both minichromosomes were generated, enabling comparative expression analysis by primer extension assays. Deletion and block substitution mutations of one of the minichromosomes revealed a TATA-like element, a putative initiator element, and two distinct upstream sequence elements (USEs). Determination of transcription initiation sites and a sequence alignment indicated that both TATA-like and initiator elements are conserved components of S. lemnae minichromosomes, whereas the USEs appear to be specific for the alpha1 tubulin minichromosome. The alpha2 tubulin minichromosome promoter is very short, comprising the two proximal elements but not the USEs. Despite the latter finding, up-regulation of alpha-tubulin expression in cells treated with concanavalin A activated the alpha2 but not the alpha1 tubulin promoter. These results therefore show that gene expression regulation in S. lemnae occurs at the level of transcription initiation on the basis of structurally different promoters.