Protist predation can favour cooperation within bacterial species

Here, we studied how protist predation affects cooperation in the opportunistic pathogen bacterium Pseudomonas aeruginosa, which uses quorum sensing (QS) cell-to-cell signalling to regulate the production of public goods. By competing wild-type bacteria with QS mutants (cheats), we show that a functioning QS system confers an elevated resistance to predation. Surprisingly, cheats were unable to exploit this resistance in the presence of cooperators, which suggests that resistance does not appear to result from activation of QS-regulated public goods. Instead, elevated resistance of wild-type bacteria was related to the ability to form more predation-resistant biofilms. This could be explained by the expression of QS-regulated resistance traits in densely populated biofilms and floating cell aggregations, or alternatively, by a pleiotropic cost of cheating where less resistant cheats are selectively removed from biofilms. These results show that trophic interactions among species can maintain cooperation within species, and have further implications for P. aeruginosa virulence in environmental reservoirs by potentially enriching the cooperative and highly infective strains with functional QS system

Observations of an Energetically Isolated Quiet Sun Transient: Evidence of Quasi-Steady Coronal Heating

Increasing evidence for coronal heating contributions from cooler solar atmospheric layers, notably quiet Sun (QS) conditions, challenges standard solar atmospheric descriptions of bright transition region (TR) emission. As such, questions to the role of dynamic QS transients in contributing to the total coronal energy budget are elevated. Using observations from the {\it Atmospheric Imaging Assembly} and {\it Heliosemic Magnetic Imager} on board the {\it Solar Dynamics Observatory}, and numerical model extrapolations of coronal magnetic fields, we investigate a dynamic QS transient energetically isolated to the TR and extruding from a common footpoint shared with two heated loop arcades. A non-casual relationship is established between episodic heating of the QS transient and wide-spread magnetic field re-organization events, while evidence is found favoring a magnetic topology typical of eruptive processes. Quasi-steady interchange reconnection events are implicated as a source of the transient's visibly bright radiative signature. We consider the QS transient's temporally stable ($\approx$\,35\,min) radiative nature occurs as a result of the large-scale magnetic field geometries of the QS and/or relatively quiet nature of the magnetic photosphere, which possibly act to inhibit energetic buildup processes required to initiate a catastrophic eruption phase. This work provides insight to the QS's thermodynamic and magnetic relation to eruptive processes quasi-steadily heating a small-scale dynamic and TR transient. This work elevates arguments of non-negligible coronal heating contributions from cool atmospheric layers in QS conditions, and increases evidence for solar wind mass feeding of dynamic transients therein.Comment: 13 pages, 9 figure

Two-Qubit Couplings of Singlet-Triplet Qubits Mediated by One Quantum State

We describe high-fidelity entangling gates between singlet-triplet qubits (STQs) which are coupled via one quantum state (QS). The QS can be provided by a quantum dot itself or by another confined system. The orbital energies of the QS are tunable using an electric gate close to the QS, which changes the interactions between the STQs independent of their single-qubit parameters. Short gating sequences exist for the controlled NOT (CNOT) operations. We show that realistic quantum dot setups permit excellent entangling operations with gate infidelities below $10^{-3}$, which is lower than the quantum error correction threshold of the surface code. We consider limitations from fabrication errors, hyperfine interactions, spin-orbit interactions, and charge noise in GaAs and Si heterostructures.Comment: 12 pages, 6 figure

Quasi-stationary distributions for the Domany-Kinzel stochastic cellular automaton

We construct the {\it quasi-stationary} (QS) probability distribution for the Domany-Kinzel stochastic cellular automaton (DKCA), a discrete-time Markov process with an absorbing state. QS distributions are derived at both the one- and two-site levels. We characterize the distribuitions by their mean, and various moment ratios, and analyze the lifetime of the QS state, and the relaxation time to attain this state. Of particular interest are the scaling properties of the QS state along the critical line separating the active and absorbing phases. These exhibit a high degree of similarity to the contact process and the Malthus-Verhulst process (the closest continuous-time analogs of the DKCA), which extends to the scaling form of the QS distribution.Comment: 15 pages, 9 figures, submited to PR

Viral quasispecies profiles as the result of the interplay of competition and cooperation

Viral quasispecies can be regarded as a swarm of genetically related mutants or a quasispecies (QS). A common formalism to approach QS is the replicator-mutator equation (RME). However, a problem with the RME is how to quantify the interaction coefficients between viral variants. Here, this is addressed by adopting an ecological perspective and resorting to the niche theory of competing communities, which assumes that the utilization of resources primarily determines ecological segregation between competing individuals (the different viral variants that constitute the QS). Using this novel combination of RME plus the ecological concept of niche overlapping, for describing QS, we explore the population distributions of viral variants that emerge, as well as the corresponding dynamics. We observe that the population distribution requires very long transients both to A) reach equilibrium and B) to show a clear dominating master sequence. Based on different independent and recent experimental evidence, we find that when some cooperation or facilitation between variants is included in appropriate doses we can solve both A) and B). We show that a useful quantity to calibrate the degree of cooperation is the Shannon entropy. Therefore, in order to get a typical quasispecies profile, it seems that pure competition is not enough. Rather, some degree of cooperation among viral variants is needed. This has several biological implications that might contribute to shed light on the mechanisms operating in QS dynamics and to understand the QS as a whole entity.Comment: 23 pages, 5 figure