Effect of increased pCO2 level on early shell development in great scallop (Pecten maximus Lamarck) larvae

As a result of high anthropogenic CO2 emissions, the concentration of CO2 in the oceans has increased, causing a decrease in pH, known as ocean acidification (OA). Numerous studies have shown negative effects on marine invertebrates, and also that the early life stages are the most sensitive to OA. We studied the effects of OA on embryos and unfed larvae of the great scallop (Pecten maximus Lamarck), at pCO(2) levels of 469 (ambient), 807, 1164, and 1599 µatm until seven days after fertilization. To our knowledge, this is the first study on OA effects on larvae of this species. A drop in pCO(2) level the first 12 h was observed in the elevated pCO(2) groups due to a discontinuation in water flow to avoid escape of embryos. When the flow was restarted, pCO(2) level stabilized and was significantly different between all groups. OA affected both survival and shell growth negatively after seven days. Survival was reduced from 45% in the ambient group to 12% in the highest pCO(2) group. Shell length and height were reduced by 8 and 15 %, respectively, when pCO(2) increased from ambient to 1599 µatm. Development of normal hinges was negatively affected by elevated pCO(2) levels in both trochophore larvae after two days and veliger larvae after seven days. After seven days, deformities in the shell hinge were more connected to elevated pCO(2) levels than deformities in the shell edge. Embryos stained with calcein showed fluorescence in the newly formed shell area, indicating calcification of the shell at the early trochophore stage between one and two days after fertilization. Our results show that P. maximus embryos and early larvae may be negatively affected by elevated pCO(2) levels within the range of what is projected towards year 2250, although the initial drop in pCO(2) level may have overestimated the effect of the highest pCO(2) levels. Future work should focus on long-term effects on this species from hatching, throughout the larval stages, and further into the juvenile and adult stages.

Aerodynamic Analysis of Open Trailing Edge Airfoils at Low Reynolds Number

A study has been made on the influence of the open trailing edge in airfoils used in different devices relating their aerodynamic performances. Wind tunnel tests have been made at different Reynolds numbers and angles of attack in order to show this effect. Besides, a quantitative study of the aerodynamic properties has been made based on the different trailing edge thickness

Influence of open trailing edge on laminar aerofoils at low Reynols number

This article deals with the effect of open trailing edge on the aerodynamic characteristics of laminar aerofoils at low Reynolds numbers, the attention being focussed on the influence of such a trailingedge imperfection on the aerodynamic efficiency. Wind tunnel tests have been performed at different Reynolds numbers and angles of attack, and global aerodynamic as well as pressure distributions were measured (in these tests two types of open trailing edges, either sharp or rounded were considered). From experimental results, a quantitative analysis of the influence of the trailing-edge thickness on the degradation of aerofoil aerodynamic performances has been obtained, which allows the establishment of a criterion for an acceptance limit for this kind of imperfection.

Effect of adhesive thickness and concrete strength on FRP-Concrete Bonds

The use of fiber-reinforced polymer (FRP) composites for strengthening, repairing, or rehabilitating concrete structures has become more and more popular in the last 10 years. Irrespective of the type of strengthening used, design is conditioned, among others, by concrete-composite bond failure, normally attributed to stress at the interface between these two materials. Single shear, double shear, and notched beam tests are the bond tests most commonly used by the scientific community to estimate bond strength, effective length, and the bond stress-slip relationship. The present paper discusses the effect of concrete strength and adhesive thickness on the results of beam tests, which reproduce debonding conditions around bending cracks much more accurately. The bond stress-slip relationship was analyzed in a cross section near the inner edge, where stress was observed to concentrate. The ultimate load and the bond stress-slip relationship were visibly affected by concrete strength. Adhesive thickness, in turn, was found to have no significant impact on low-strength concrete but a somewhat greater effect on higher strength materials.

Influence of leading edge imperfections on the aerodynamic characterictics of NACA 632-215 laminar aerofoils at low Reynolds number

This article deals with the effect of leading edge imperfections on the aerodynamic characteristics of a NACA 632-215 laminar aerofoil at low Reynolds numbers. Wind tunnel tests have been performed at different Reynolds numbers and angles of attack and global aerodynamic loads were measured. To perform these tests, a NACA 632-215 aerofoil was built up in two halves (corresponding to the upper side and to the lower side), the leading edge imperfection here considered being a slight displacement of half aerofoil with respect to the other. From experimental results, a quantitative measure of the influence of the leading edge displacement on the degradation of the aerofoil aerodynamic performances has been obtained. This allows the establishment of a criterion for an acceptance limit for this kind of imperfection

Aerodynamic Study of Airfoils with Leading Edge Imperfections at Low Reynolds Number

A study has been made on the influence of the leading edge imperfections in airfoils used in different devices relating their aerodynamic performances. Wind tunnel tests have been made at different Reynolds numbers and angle of attacks in order to show this effect. Later, a quantitative study of the aerodynamic properties has been made based on the different leading edge imperfections and their size.

Spin-filtered edge states in graphene

Spin–orbit coupling changes graphene, in principle, into a two-dimensional topological insulator, also known as quantum spin Hall insulator. One of the expected consequences is the existence of spin-filtered edge states that carry dissipationless spin currents and undergo no backscattering in the presence of non-magnetic disorder, leading to quantization of conductance. Whereas, due to the small size of spin–orbit coupling in graphene, the experimental observation of these remarkable predictions is unlikely, the theoretical understanding of these spin-filtered states is shedding light on the electronic properties of edge states in other two-dimensional quantum spin Hall insulators. Here we review the effect of a variety of perturbations, like curvature, disorder, edge reconstruction, edge crystallographic orientation, and Coulomb interactions on the electronic properties of these spin filtered states.

Quantum Hall effect in gapped graphene heterojunctions

We model the quantum Hall effect in heterostructures made of two gapped graphene stripes with different gaps, Δ1 and Δ2. We consider two main situations, Δ1=0,Δ2≠0, and Δ1=−Δ2. They are different in a fundamental aspect: only the latter features kink states that, when intervalley coupling is absent, are protected against backscattering. We compute the two-terminal conductance of heterostructures with channel length up to 430 nm, in two transport configurations, parallel and perpendicular to the interface. By studying the effect of disorder on the transport along the boundary, we quantify the robustness of kink states with respect to backscattering. Transport perpendicular to the boundary shows how interface states open a backscattering channel for the conducting edge states, spoiling the perfect conductance quantization featured by the homogeneously gapped graphene Hall bars. Our results can be relevant for the study of graphene deposited on hexagonal boron-nitride, as well as to model graphene with an interaction-driven gapped phase with two equivalent phases separated by a domain wall.

Quantum anomalous Hall effect in graphene coupled to skyrmions

Skyrmions are topologically protected spin textures, characterized by a topological winding number N, that occur spontaneously in some magnetic materials. Recent experiments have demonstrated the capability to grow graphene on top Fe/Ir, a system that exhibits a two-dimensional skyrmion lattice. Here we show that a weak exchange coupling between the Dirac electrons in graphene and a two-dimensional skyrmion lattice withN = ±1 drives graphene into a quantum anomalous Hall phase, with a band gap in bulk, a Chern number C = 2N, and chiral edge states with perfect quantization of conductance G = 2N e2 h . Our findings imply that the topological properties of the skyrmion lattice can be imprinted in the Dirac electrons of graphene.

Edge states in graphene-like systems

The edges of graphene and graphene like systems can host localized states with evanescent wave function with properties radically different from those of the Dirac electrons in bulk. This happens in a variety of situations, that are reviewed here. First, zigzag edges host a set of localized non-dispersive state at the Dirac energy. At half filling, it is expected that these states are prone to ferromagnetic instability, causing a very interesting type of edge ferromagnetism. Second, graphene under the influence of external perturbations can host a variety of topological insulating phases, including the conventional quantum Hall effect, the quantum anomalous Hall (QAH) and the quantum spin Hall phase, in all of which phases conduction can only take place through topologically protected edge states. Here we provide an unified vision of the properties of all these edge states, examined under the light of the same one orbital tight-binding model. We consider the combined action of interactions, spin–orbit coupling and magnetic field, which produces a wealth of different physical phenomena. We briefly address what has been actually observed experimentally.

Mesoscopic one-way channels for quantum state transfer via the quantum hall effect

We show that the one-way channel formalism of quantum optics has a physical realization in electronic systems. In particular, we show that magnetic edge states form unidirectional quantum channels capable of coherently transporting electronic quantum information. Using the equivalence between one-way photonic channels and magnetic edge states, we adapt a proposal for quantum state transfer to mesoscopic systems using edge states as a quantum channel, and show that it is feasible with reasonable experimental parameters. We discuss how this protocol may be used to transfer information encoded in number, charge, or spin states of quantum dots, so it may prove useful for transferring quantum information between parts of a solid-state quantum computer

Analysis of the effect of different NKT cell subpopulations on the activation of CD4 and CD8 T cells, NK cells, and B cells

Objective. NKT cells have diverse immune regulatory functions including activation of cells involved in Th1- and Th2-type immune activities. Most previous studies have investigated the functions of NKT cells as a single family but more recent evidence indicates the distinct functional properties of NKT cell subpopulation. This study aims to determine whether NKT cell subpopulations have different stimulatory activities on other immune cells that may affect the outcome of NKT cell-based immunotherapy. Methods. NKT cells and NKT cell subpopulations (CD4(+)CD8(-), CD4(-)CD8(+), CD4(-)CD8(+)) were cocultured with PBMC and their activities on immune cells including CD4(+) and CD8(+) T cells, NK cells, and B cells were assessed by flow cytometry. The production of cytokines in culture was measured by enzyme-linked immunsorbent assay. Results. The CD4(+)CD8(-) NKT cells demonstrated substantially greater stimulatory activities on CD4(+) T cells, NK cells, and B cells than other NKT cell subsets. The CD4(-)CD8(+) NKT cells showed the greatest activity on CD8(+) T cells, and were the only NKT cell subset that activated these immune cells. The CD4(-)CD8(-) NKT cells showed moderate stimulatory activity on CD4(+) T cells and the least activity on other immune cells. Conclusion. The results here suggest that NKT cell subpopulations differ in their abilities to stimulate other immune cells. This highlights the potential importance of manipulating specific NKT cell subpopulations for particular therapeutic situations and of evaluating subpopulations, rather than NKT cells as a group, during investigation of a possible role of NKT cells in various disease settings. (c) 2006 International Society for Experimental Hematology. Published by Elsevier Inc.

Mach edges: a critical test of the nonlinear 3rd derivative model for edge-detection

Feature detection is a crucial stage of visual processing. In previous feature-marking experiments we found that peaks in the 3rd derivative of the luminance profile can signify edges where there are no 1st derivative peaks nor 2nd derivative zero-crossings (Wallis and George 'Mach edges' (the edges of Mach bands) were nicely predicted by a new nonlinear model based on 3rd derivative filtering. As a critical test of the model, we now use a new class of stimuli, formed by adding a linear luminance ramp to the blurred triangle waves used previously. The ramp has no effect on the second or higher derivatives, but the nonlinear model predicts a shift from seeing two edges to seeing only one edge as the added ramp gradient increases. In experiment 1, subjects judged whether one or two edges were visible on each trial. In experiment 2, subjects used a cursor to mark perceived edges and bars. The position and polarity of the marked edges were close to model predictions. Both experiments produced the predicted shift from two to one Mach edge, but the shift was less complete than predicted. We conclude that the model is a useful predictor of edge perception, but needs some modification.

Third-derivative filters predict edge locations in spatial vision

Edge detection is crucial in visual processing. Previous computational and psychophysical models have often used peaks in the gradient or zero-crossings in the 2nd derivative to signal edges. We tested these approaches using a stimulus that has no such features. Its luminance profile was a triangle wave, blurred by a rectangular function. Subjects marked the position and polarity of perceived edges. For all blur widths tested, observers marked edges at or near 3rd derivative maxima, even though these were not 1st derivative maxima or 2nd derivative zero-crossings, at any scale. These results are predicted by a new nonlinear model based on 3rd derivative filtering. As a critical test, we added a ramp of variable slope to the blurred triangle-wave luminance profile. The ramp has no effect on the (linear) 2nd or higher derivatives, but the nonlinear model predicts a shift from seeing two edges to seeing one edge as the ramp gradient increases. Results of two experiments confirmed such a shift, thus supporting the new model. [Supported by the Engineering and Physical Sciences Research Council].

Added luminance ramp alters perceived edge blur and contrast:A critical test for derivative-based models of edge coding

In many models of edge analysis in biological vision, the initial stage is a linear 2nd derivative operation. Such models predict that adding a linear luminance ramp to an edge will have no effect on the edge's appearance, since the ramp has no effect on the 2nd derivative. Our experiments did not support this prediction: adding a negative-going ramp to a positive-going edge (or vice-versa) greatly reduced the perceived blur and contrast of the edge. The effects on a fairly sharp edge were accurately predicted by a nonlinear multi-scale model of edge processing [Georgeson, M. A., May, K. A., Freeman, T. C. A., & Hesse, G. S. (in press). From filters to features: Scale-space analysis of edge and blur coding in human vision. Journal of Vision], in which a half-wave rectifier comes after the 1st derivative filter. But we also found that the ramp affected perceived blur more profoundly when the edge blur was large, and this greater effect was not predicted by the existing model. The model's fit to these data was much improved when the simple half-wave rectifier was replaced by a threshold-like transducer [May, K. A. & Georgeson, M. A. (2007). Blurred edges look faint, and faint edges look sharp: The effect of a gradient threshold in a multi-scale edge coding model. Vision Research, 47, 1705-1720.]. This modified model correctly predicted that the interaction between ramp gradient and edge scale would be much larger for blur perception than for contrast perception. In our model, the ramp narrows an internal representation of the gradient profile, leading to a reduction in perceived blur. This in turn reduces perceived contrast because estimated blur plays a role in the model's estimation of contrast. Interestingly, the model predicts that analogous effects should occur when the width of the window containing the edge is made narrower. This has already been confirmed for blur perception; here, we further support the model by showing a similar effect for contrast perception. © 2007 Elsevier Ltd. All rights reserved.