Global assessment of the status of coral reef herbivorous fishes: evidence for fishing effects.

On coral reefs, herbivorous fishes consume benthic primary producers and regulate competition between fleshy algae and reef-building corals. Many of these species are also important fishery targets, yet little is known about their global status. Using a large-scale synthesis of peer-reviewed and unpublished data, we examine variability in abundance and biomass of herbivorous reef fishes and explore evidence for fishing impacts globally and within regions. We show that biomass is more than twice as high in locations not accessible to fisheries relative to fisheries-accessible locations. Although there are large biogeographic differences in total biomass, the effects of fishing are consistent in nearly all regions. We also show that exposure to fishing alters the structure of the herbivore community by disproportionately reducing biomass of large-bodied functional groups (scraper/excavators, browsers, grazer/detritivores), while increasing biomass and abundance of territorial algal-farming damselfishes (Pomacentridae). The browser functional group that consumes macroalgae and can help to prevent coral-macroalgal phase shifts appears to be most susceptible to fishing. This fishing down the herbivore guild probably alters the effectiveness of these fishes in regulating algal abundance on reefs. Finally, data from remote and unfished locations provide important baselines for setting management and conservation targets for this important group of fishes.

Fluctuation-driven magnetic hard-axis ordering in metallic ferromagnets.

We demonstrate that the interplay between soft electronic particle-hole fluctuations and magnetic anisotropies can drive ferromagnetic moments to point along a magnetic hard axis. As a proof of concept, we show this behavior explicitly for a generic two-band model with local Coulomb and Hund's interactions and a spin-orbit-induced easy plane anisotropy. The phase diagram is calculated within the fermionic quantum order-by-disorder approach, which is based on a self-consistent free-energy expansion around a magnetically ordered state with unspecified orientation. Quantum fluctuations render the transition of the easy-plane ferromagnet first order below a tricritical point. At even lower temperatures, directionally dependent transverse fluctuations dominate the magnetic anisotropy, and the moments flip to lie along the magnetic hard axis. We discuss our findings in the context of recent experiments that show this unusual ordering along the magnetic hard direction.

Phase transitions in the classical simulability of open quantum systems.

We introduce a Langevin unravelling of the density matrix evolution of an open quantum system over matrix product states, which we term the time-dependent variational principle-Langevin equation. This allows the study of entanglement dynamics as a function of both temperature and coupling to the environment. As the strength of coupling to and temperature of the environment is increased, we find a transition where the entanglement of the individual trajectories saturates, permitting a classical simulation of the system for all times. This is the Hamiltonian open system counterpart of the saturation in entanglement found in random circuits with projective or weak measurements. If a system is open, there is a limit to the advantage in simulating its behaviour on a quantum computer, even when that evolution harbours important quantum effects. Moreover, if a quantum simulator is in this phase, it cannot simulate with quantum advantage.

Strain control of a bandwidth-driven spin reorientation in Ca3Ru2O7.

The layered-ruthenate family of materials possess an intricate interplay of structural, electronic and magnetic degrees of freedom that yields a plethora of delicately balanced ground states. This is exemplified by Ca3Ru2O7, which hosts a coupled transition in which the lattice parameters jump, the Fermi surface partially gaps and the spins undergo a 90∘ in-plane reorientation. Here, we show how the transition is driven by a lattice strain that tunes the electronic bandwidth. We apply uniaxial stress to single crystals of Ca3Ru2O7, using neutron and resonant x-ray scattering to simultaneously probe the structural and magnetic responses. These measurements demonstrate that the transition can be driven by externally induced strain, stimulating the development of a theoretical model in which an internal strain is generated self-consistently to lower the electronic energy. We understand the strain to act by modifying tilts and rotations of the RuO6 octahedra, which directly influences the nearest-neighbour hopping. Our results offer a blueprint for uncovering the driving force behind coupled phase transitions, as well as a route to controlling them.

Hawking radiation and nonequilibrium quantum critical current noise.

The dynamical scaling of quantum critical systems in thermal equilibrium may be inherited in the driven steady state, leading to universal out-of-equilibrium behavior. This attractive notion has been demonstrated in just a few cases. We demonstrate how holography-a mapping between the quantum critical system and a gravity dual-provides an illuminating perspective and new results. Nontrivial out-of-equilibrium universality is particularly apparent in current noise, which is dual to Hawking radiation in the gravitational system. We calculate this in a two-dimensional system driven by a strong in-plane electric field and deduce a universal scaling function interpolating between previously established equilibrium and far-from-equilibrium current noise. Since this applies at all fields, out-of-equilibrium experiments no longer require very high fields for comparison with theory.

Simulating groundstate and dynamical quantum phase transitions on a superconducting quantum computer.

The phenomena of quantum criticality underlie many novel collective phenomena found in condensed matter systems. They present a challenge for classical and quantum simulation, in part because of diverging correlation lengths and consequently strong finite-size effects. Tensor network techniques that work directly in the thermodynamic limit can negotiate some of these difficulties. Here, we optimise a translationally invariant, sequential quantum circuit on a superconducting quantum device to simulate the groundstate of the quantum Ising model through its quantum critical point. We further demonstrate how the dynamical quantum critical point found in quenches of this model across its quantum critical point can be simulated. Our approach avoids finite-size scaling effects by using sequential quantum circuits inspired by infinite matrix product states. We provide efficient circuits and a variety of error mitigation strategies to implement, optimise and time-evolve these states.

Inhomogeneous phase formation on the border of itinerant ferromagnetism.

A variety of analytical techniques suggest that quantum fluctuations lead to a fundamental instability of the Fermi liquid that drives ferromagnetic transitions first order at low temperatures. We present both analytical and numerical evidence that, driven by the same quantum fluctuations, this first order transition is preempted by the formation of an inhomogeneous magnetic phase. This occurs in a manner that is closely analogous to the formation of the inhomogeneous superconducting Fulde-Ferrel-Larkin-Ovchinnikov state. We derive these results from a field-theoretical approach supplemented with numerical quantum Monte Carlo simulations.

The Lyapunov spectra of quantum thermalisation.

Thermalisation in closed quantum systems occurs through a process of dephasing due to parts of the system outside of the window of observation, gradually revealing the underlying thermal nature of eigenstates. In contrast, closed classical systems thermalize due to dynamical chaos. We demonstrate a deep link between these processes. Projecting quantum dynamics onto variational states using the time-dependent variational principle, results in classical chaotic Hamiltonian dynamics. We study an infinite spin chain in two ways-using the matrix product state ansatz for the wavefunction and for the thermofield purification of the density matrix-and extract the full Lyapunov spectrum of the resulting dynamics. We show that the entanglement growth rate is related to the Kolmogorov-Sinai entropy of dynamics projected onto states with appropriate entanglement, extending previous results about initial entanglement growth to all times. The Lyapunov spectra for thermofield descriptions of thermalizing systems show a remarkable semi-circular distribution.

Schrödinger equation with a spatially and temporally random potential: effects of cross-phase modulation in optical communication.

We model the effects of cross-phase modulation in frequency (or wavelength) division multiplexed optical communications systems, using a Schrödinger equation with a spatially and temporally random potential. Green's functions for the propagation of light in this system are calculated using Feynman path-integral and diagrammatic techniques. This propagation leads to a non-Gaussian joint distribution of the input and output optical fields. We use these results to determine the amplitude and timing jitter of a signal pulse and to estimate the system capacity in analog communication.

Insurance--a dental viewpoint. Part I: An introduction.

Current changes in the market are likely to alter our perception of insurance companies and brokers. Brokers will soon be required to disclose the amounts of commission earned and this may drive individuals back into the arms of the salesmen from individual companies. This series of articles sets out to show the options that are available to the dentist and to show how to use the range of expert advice available.

Insurance--a dental viewpoint. Part II: Sickness and accident.

It is a very fortunate dentist indeed who survives an average 40-year working life without suffering illness or an accident. This will normally keep the dentist away from work and the ability to earn for a period of time. In the worst cases the disability may prevent a return to normal work with disastrous effects upon career earnings. Insurance against loss of earnings has therefore a very high priority.

Insurance--a dental viewpoint. Part III: Life assurance, pensions and annuities.

The insurance market is complex and there can be serious taxation implications in many decisions. The tax aspect may be beneficial to the dentist or it can have serious consequences. The advice of independent experts in accountancy and insurance is often vital if catastrophic pitfalls are to be avoided.

Insurance--a dental viewpoint. Part IV: Professional risks indemnity.

Over the last decade professional practice has changed in many ways, not least in the willingness of patients to seek damages. The treasurer of the Medical Defence Union, in his report on the year 1989, stated that claims paid out on behalf of doctors in Britain doubled in frequency and the average amount awarded also doubled between 1985 and 1988, subscription rates increased fourfold. By contrast, 40 years ago life membership of a 'defence organisation' was available for less that an annual subscription today.

Regrets.

A year or so ago I was invited by an Italian dentist to spend a day with him in his practice and to attend a two-day seminar, which he was presenting. The location, in the mountains near to Lake Como and the Swiss border, was enough to persuade me to accept. However I was to find out that the professional aspects of the trip were not only most invigorating but that they would also cause me to look back with concern to my own career. Had I done as well for my patients, my family and myself as I could have done?

Disopyramide--an effective treatment for lignocaine resistant ventricular dysrhythmias.

Intravenous disopyramide was used in 13 patients who developed recurrent ventricular dysrhythmias despite initial treatment with intravenous lignocaine after admission to the Coronary Care Unit of a busy district hospital. This was effective in 8 of the 13 patients treated and there was no major side effects observed. Disopyramide has the advantage of being available both as an oral and an intravenous preparation and is a useful drug to be added to the list of more conventional anti-dysrhythmic agents.

Feeling-of-knowing judgments and strategy selection in spelling.

Metacognitive processes, such as monitoring one's knowledge and selecting appropriate strategies, may be important in skilled spelling. We hypothesized that skilled spellers have knowledge of which words they know how to spell and also that the accuracy with which people monitor their knowledge should be related to the spelling strategies they select. College students provided Feeling-of-Knowing ratings about the spellings of words and also spelled the same words and indicated whether they sounded out or remembered the spellings. Feeling-of-Knowing ratings were moderately correlated with Spelling Accuracy and were more strongly predictive of Spelling Accuracy when Feeling-of-Knowing ratings and spellings were done as part of the same task rather than as separate tasks. Analyses indicate that those who were better at monitoring their knowledge of spelling also chose more congruent spelling strategies. The results suggest that skilled spellers can monitor which words they know how to spell, but this ability to monitor is far from perfect and varies considerably. Further, the results suggest that ability to monitor spelling knowledge is related to strategy selection in spelling.

Canadian immigration policy: the effectiveness of the point system and other instruments.

"This paper examines the effects of changes in Canadian immigration policy on the occupational composition of immigration. We focus on 1967 changes that created a regulatory system, including the point system, that still forms the framework of Canadian immigration policy. We find that the point system provides some control over occupational composition but that its effectiveness in fine tuning is limited by the large number of other characteristics it seeks to control. We also find that entry class and source country composition of inflow have impacts that have swamped the effects of the point system in the last two decades." (SUMMARY IN FRE)