A stratified transect approach captures reef complexity with canopy-forming organisms

On the Great Barrier Reef (GBR), persistent changes to reef communities have begun to be documented, and on inshore reefs these shifts may favour the proliferation of macroalgae. Critical to understanding changes to reef community structure in response to anthropogenic impacts is developing effective methods to accurately document the abundance of different reef organisms. Effective monitoring must be time and cost efficient, replicable, and able to sufficiently and accurately detect disturbances to allow development of strategies to mitigate their impacts. Traditional techniques to document coral reef communities (i.e. photo-quadrats, benthic intercept transects) rely on planar views, which tend to either over- or under-represent canopy-forming organisms. As canopy-forming organisms are likely to be affected by anthropogenic influences (corals negatively, algae positively), it is essential for monitoring programs to implement methods sufficient to document changes to the vertical dimension of coral reefs. Here we build on previous work to document the canopy effect in coral-dominated ecosystems and propose a new survey approach suitable for implementation in algal-dominated systems. A vertically stratified transect, modified from a traditional point intercept transect, captures benthic and canopy-forming members of reef communities and provides information on three-dimensional complexity. To test the capability of the new method to detect changes in vertical reef structure, seaweed was removed from experimental quadrats and monitoring techniques were applied before and after four months of regrowth. A stratified method more accurately captured the three-dimensional change resulting from algal canopy growth, while resolving the over- and under-representation of algal biomass in two traditional techniques. We propose that a stratified transect method improves abundance estimates of canopy-forming organisms whilst maintaining data compatibility with traditional methods

Modular termination verification for non-blocking concurrency

© Springer-Verlag Berlin Heidelberg 2016.We present Total-TaDA, a program logic for verifying the total correctness of concurrent programs: that such programs both terminate and produce the correct result. With Total-TaDA, we can specify constraints on a thread’s concurrent environment that are necessary to guarantee termination. This allows us to verify total correctness for nonblocking algorithms, e.g. a counter and a stack. Our specifications can express lock- and wait-freedom. More generally, they can express that one operation cannot impede the progress of another, a new non-blocking property we call non-impedance. Moreover, our approach is modular. We can verify the operations of a module independently, and build up modules on top of each other

Charge separation in donor-C60 complexes with real-time Green's functions: The importance of nonlocal correlations

We use the Nonequilibrium Green's Function (NEGF) method to perform real-time simulations of the ultrafast electron dynamics of photoexcited donor-C60 complexes modeled by a Pariser-Parr-Pople Hamiltonian. The NEGF results are compared to mean-field Hartree-Fock (HF) calculations to disentangle the role of correlations. Initial benchmarking against numerically highly accurate time-dependent Density Matrix Renormalization Group calculations verifies the accuracy of NEGF. We then find that charge-transfer (CT) excitons partially decay into charge separated (CS) states if dynamical non-local correlation corrections are included. This CS process occurs in ~10 fs after photoexcitation. In contrast, the probability of exciton recombination is almost 100% in HF simulations. These results are largely unaffected by nuclear vibrations; the latter become however essential whenever level misalignment hinders the CT process. The robust nature of our findings indicate that ultrafast CS driven by correlation-induced decoherence may occur in many organic nanoscale systems, but it will only be correctly predicted by theoretical treatments that include time-nonlocal correlations.Comment: 9 pages, 6 figures + supplemental information (4 pages)

Ultrathin Metallic Coatings Can Induce Quantum Levitation between Nanosurfaces

There is an attractive Casimir-Lifshitz force between two silica surfaces in a liquid (bromobenze or toluene). We demonstrate that adding an ultrathin (5-50{\AA}) metallic nanocoating to one of the surfaces results in repulsive Casimir-Lifshitz forces above a critical separation. The onset of such quantum levitation comes at decreasing separations as the film thickness decreases. Remarkably the effect of retardation can turn attraction into repulsion. From that we explain how an ultrathin metallic coating may prevent nanoelectromechanical systems from crashing together.Comment: 4 pages, 5 figure

Duplex Scanning as the Sole Preoperative Imaging Method for Infrainguinal Arterial Surgery

AbstractObjective: to evaluate preoperative duplex as the sole investigation prior to lower limb reconstruction. Design retrospective analysis. Material and methods: between January 1995 and December 1999, 157 of 329 surgical interventions for chronic infrainguinal arterial or aneurysmal disease were performed without preoperative angiography.Results : in patients undergoing femoral artery endarterectomy, the extent of the stenosis and the status of the distal deep femoral artery were correctly diagnosed with duplex scanning in all but one patient. Duplex scan findings in patients undergoing infrainguinal bypass procedures were in agreement with the findings obtained from on-table angiography in regard to the selection of optimal outflow anastomotic sites in 123 (98%). Duplex scanning correctly evaluated the status of runoff in 113 (90%). There were no significant differences in 30-day occlusion rate and patency at 12 months between reconstructions performed with and without preoperative angiography. Conclusion: in patients with conclusive duplex scan findings there is no need to perform angiography prior to lower limb reconstruction

Hitching a ride on Hercules:fatal epibiosis drives ecosystem change from mud banks to oyster reefs

[Excerpt] Best known as a "love them or hate them" luxury food, or for their pearls, oysters are also ecosystem engineers, forming vast oyster reefs. Oyster reefs provide habitat for a myriad of species, and support fisheries, improve water quality and provide coastal protection. These services are estimated to be worth US$5,500–$99,000 per hectare per year (Grabowski et al. 2012). Globally, oyster reefs have declined by 85% through destructive overfishing, coastal development, pollution, and introduced competitors, predators and diseases (Beck et al. 2011). Active restoration is becoming an increasingly popular tool to bring back lost oyster reefs and the ecosystem services they provide (Fitzsimons et al. 2019). However, restoration is not always successful, and knowledge about how reefs naturally form and function is vital to improve restoration success. Oyster larvae only settle on hard substrates. Reefs proliferate because oyster shells provide a settlement surface, and oysters provide chemical and sound cues that facilitate larval settlement (Lillis et al. 2013). However, these reefs often form on intertidal sand and mud banks. This raises the question, how do oyster reefs form on mud banks in the absence of hard surfaces

Consistency of shared reference frames should be reexamined

In a recent Letter [G. Chiribella et al., Phys. Rev. Lett. 98, 120501 (2007)], four protocols were proposed to secretly transmit a reference frame. Here We point out that in these protocols an eavesdropper can change the transmitted reference frame without being detected, which means the consistency of the shared reference frames should be reexamined. The way to check the above consistency is discussed. It is shown that this problem is quite different from that in previous protocols of quantum cryptography.Comment: 3 pages, 1 figure, comments are welcom

Fisher Information for Inverse Problems and Trace Class Operators

This paper provides a mathematical framework for Fisher information analysis for inverse problems based on Gaussian noise on infinite-dimensional Hilbert space. The covariance operator for the Gaussian noise is assumed to be trace class, and the Jacobian of the forward operator Hilbert-Schmidt. We show that the appropriate space for defining the Fisher information is given by the Cameron-Martin space. This is mainly because the range space of the covariance operator always is strictly smaller than the Hilbert space. For the Fisher information to be well-defined, it is furthermore required that the range space of the Jacobian is contained in the Cameron-Martin space. In order for this condition to hold and for the Fisher information to be trace class, a sufficient condition is formulated based on the singular values of the Jacobian as well as of the eigenvalues of the covariance operator, together with some regularity assumptions regarding their relative rate of convergence. An explicit example is given regarding an electromagnetic inverse source problem with "external" spherically isotropic noise, as well as "internal" additive uncorrelated noise.Comment: Submitted to Journal of Mathematical Physic

Retardation turns the van der Waals attraction into Casimir repulsion already at 3 nm

Casimir forces between surfaces immersed in bromobenzene have recently been measured by Munday et al. Attractive Casimir forces were found between gold surfaces. The forces were repulsive between gold and silica surfaces. We show the repulsion is due to retardation effects. The van der Waals interaction is attractive at all separations. The retardation driven repulsion sets in already at around 3 nm. To our knowledge retardation effects have never been found at such a small distance before. Retardation effects are usually associated with large distances

Sign of the Casimir-Polder interaction between atoms and oil-water interfaces: Subtle dependence on dielectric properties

We demonstrate that Casimir-Polder energies between noble gas atoms (dissolved in water) and oil-water interfaces are highly surface specific. Both repulsion (e.g. hexane) and attraction (e.g. glycerine and cyclodecane) is found with different oils. For several intermediate oils (e.g. hexadecane, decane, and cyclohexane) both attraction and repulsion can be found in the same system. Near these oil-water interfaces the interaction is repulsive in the non-retarded limit and turns attractive at larger distances as retardation becomes important. These highly surface specific interactions may have a role to play in biological systems where the surface may be more or less accessible to dissolved atoms.Comment: 5 pages, 6 figure