Reflection and Transmission at a Phase Discontinuous Interface

In this paper we extend the derivation of the modified form Snells's law that occurs when an additional phase profile is introduced at the material interface. We show that this permits electromagnetic (EM) beam steering, negative refraction and retrodirective action opportunities for such engineered surfaces even if they are immersed in a uniform dielectric. Simple expressions for the retrodirected and negatively refracted beams are derived along with the propagation conditions that occur at the boundary interface inside the critical angle range. It is also demonstrated how the transmission and reflected power levels are affected by the additional phase taper introduced at the surface.

In search of common grounds: Stitching the divided landscape of urban parks in Belfast's interface zones

Political and spatial contestation in divided cities contributes to strategies of self-defense that utilize physical and spatial settings to enable the constitution of social boundaries, borders and territories.
Urban parks that are designed to ease division through an open transitional landscape can instead facilitate further segregation through their spatial order and facility layout. This paper investigates the role of the spatial design and material landscape of integrated parks in Belfast interface areas as instruments of engagement or division. It does so by analyzing the spatial organization of the parks’ facilities and the resultant ‘social voids.’ Space, time and distance were found to be effective tools for the negotiation of privacy, the manifestation of power, and the interplay of dominance and self-confidence. In the context of a divided city, strong community-culture tends to reproduce new boundaries and territories within the shared landscape. Through user interviews and spatial analysis, this paper outlines the design principles that influence spatial behavior in the urban parks of contested urban landscapes. It argues that despite granting equal access to shared public facilities, social voids and physical gaps can instill practices of division that deepen territorial barriers, both psychologically and spatially.

Probing charge screening dynamics and electrochemical processes at the solid–liquid interface with electrochemical force microscopy

The presence of mobile ions complicates the implementation of voltage-modulated scanning probe microscopy techniques such as Kelvin probe force microscopy (KPFM). Overcoming this technical hurdle, however, provides a unique opportunity to probe ion dynamics and electrochemical processes in liquid environments and the possibility to unravel the underlying mechanisms behind important processes at the solid–liquid interface, including adsorption, electron transfer and electrocatalysis. Here we describe the development and implementation of electrochemical force microscopy (EcFM) to probe local bias- and time-resolved ion dynamics and electrochemical processes at the solid–liquid interface. Using EcFM, we demonstrate contact potential difference measurements, consistent with the principles of open-loop KPFM operation. We also demonstrate that EcFM can be used to investigate charge screening mechanisms and electrochemical reactions in the probe–sample junction. We further establish EcFM as a force-based imaging mode, allowing visualization of the spatial variability of sample-dependent local electrochemical properties.

Effect of the crown design and interface lute parameters on the stress-state of a machined crown-tooth system: A finite element analysis

The effect of preparation design and the physical properties of the interface lute on the restored machined ceramic crown-tooth complex are poorly understood. The aim of this work was to determine, by means of three-dimensional finite element analysis (3D FEA) the effect of the tooth preparation design and the elastic modulus of the cement on the stress state of the cemented machined ceramic crown-tooth complex. The three-dimensional structure of human premolar teeth, restored with adhesively cemented machined ceramic crowns, was digitized with a micro-CT scanner. An accurate, high resolution, digital replica model of a restored tooth was created. Two preparation designs, with different occlusal morphologies, were modeled with cements of 3 different elastic moduli. Interactive medical image processing software (mimics and professional CAD modeling software) was used to create sophisticated digital models that included the supporting structures; periodontal ligament and alveolar bone. The generated models were imported into an FEA software program (hypermesh version 10.0, Altair Engineering Inc.) with all degrees of freedom constrained at the outer surface of the supporting cortical bone of the crown-tooth complex. Five different elastic moduli values were given to the adhesive cement interface 1.8 GPa, 4 GPa, 8 GPa, 18.3 GPa and 40 GPa; the four lower values are representative of currently used cementing lutes and 40 GPa is set as an extreme high value. The stress distribution under simulated applied loads was determined. The preparation design demonstrated an effect on the stress state of the restored tooth system. The cement elastic modulus affected the stress state in the cement and dentin structures but not in the crown, the pulp, the periodontal ligament or the cancellous and cortical bone. The results of this study suggest that both the choice of the preparation design and the cement elastic modulus can affect the stress state within the restored crown-tooth complex.

Optomechanical interface for probing matter-wave coherence

We combine matter-wave interferometry and cavity optomechanics to propose a coherent matter-light interface based on mechanical motion at the quantum level. We demonstrate a mechanism that is able to transfer non-classical features imprinted on the state of a matter-wave system to an optomechanical device, transducing them into distinctive interference fringes. This provides a reliable tool for the inference of quantum coherence in the particle beam. Moreover, we discuss how our system allows for intriguing perspectives, paving the way to the construction of a device for the encoding of quantum information in matter-wave systems. Our proposal, which highlights previously unforeseen possibilities for the synergistic exploitation of these two experimental platforms, is explicitly based on existing technology, available and widely used in current cutting-edge experiments.

Microbial community of the deep-sea brine Lake Kryos seawater-brine interface is active below the chaotropicity limit of life as revealed by recovery of mRNA

Within the complex of deep, hypersaline anoxic lakes (DHALs) of the Mediterranean Ridge, we identified a new, unexplored DHAL and named it ‘Lake Kryos’ after a nearby depression. This lake is filled with magnesium chloride (MgCl2)-rich, athalassohaline brine (salinity > 470 practical salinity units), presumably formed by the dissolution of Messinian bischofite. Compared with the DHAL Discovery, it contains elevated concentrations of kosmotropic sodium and sulfate ions, which are capable of reducing the net chaotropicily of MgCl2-rich solutions. The brine of Lake Kryos may therefore be biologically permissive at MgCl2 concentrations previously considered incompatible with life. We characterized the microbiology of the seawater–Kryos brine interface and managed to recover mRNA from the 2.27–3.03 MMgCl2 layer (equivalent to 0.747–0.631 water activity), thereby expanding the established chaotropicity window-for-life. The primary bacterial taxa present there were Kebrit Deep Bacteria 1 candidate division and DHAL-specific group of organisms, distantly related toDesulfohalobium. Two euryarchaeal candidate divisions, Mediterranean Sea Brine Lakes group 1 and halophilic cluster 1, accounted for > 85% of the rRNA-containing archaeal clones derived from the 2.27–3.03 M MgCl2 layer, but were minority community-members in the overlying interface-layers. These findings shed light on the plausibility of life in highly chaotropic environments, geochemical windows for microbial extremophiles, and have implications for habitability elsewhere in the Solar System.

Element-specific depth profile of magnetism and stoichiometry at the La0.67Sr0.33MnO3/BiFeO3 interface

Depth-sensitive magnetic, structural and chemical characterization is important in the understanding and optimization of novel physical phenomena emerging at interfaces of transition metal oxide heterostructures. In a simultaneous approach we have used polarized neutron and resonant X-ray reflectometry to determine the magnetic profile across atomically sharp interfaces of ferromagnetic La0.67Sr0.33MnO3 / multiferroic BiFeO3 bi-layers with sub-nanometer resolution. In particular, the X-ray resonant magnetic reflectivity measurements at the Fe and Mn resonance edges allowed us to determine the element specific depth profile of the ferromagnetic moments in both the La0.67Sr0.33MnO3 and BiFeO3 layers. Our measurements indicate a magnetically diluted interface layer within the La0.67Sr0.33MnO3 layer, in contrast to previous observations on inversely deposited layers. Additional resonant X-ray reflection measurements indicate a region of an altered Mn- and O-content at the interface, with a thickness matching that of the magnetic diluted layer, as origin of the reduction of the magnetic moment.

Effects of particle/matrix interface and strengthening mechanisms on the mechanical properties of metal matrix composites

A randomly distributed multi-particle model considering the effects of particle/matrix interface and strengthening mechanisms introduced by the particles has been constructed. Particle shape, distribution, volume fraction and the particles/matrix interface due to the factors including element diffusion were considered in the model. The effects of strengthening mechanisms, caused by the introduction of particles on the mechanical properties of the composites, including grain refinement strengthening, dislocation strengthening and Orowan strengthening, are incorporated. In the model, the particles are assumed to have spheroidal shape, with uniform distribution of the centre, long axis length and inclination angle. The axis ratio follows a right half-normal distribution. Using Monte Carlo method, the location and shape parameters of the spheroids are randomly selected. The particle volume fraction is calculated using the area ratio of the spheroids. Then, the effects of particle/matrix interface and strengthening mechanism on the distribution of Mises stress and equivalent strain and the flow behaviour for the composites are discussed.

Sub-nA spatially resolved conductivity profiling of surface and interface defects in ceria films

Spatial variability of conductivity in ceria is explored using scanning probe microscopy (SPM) with galvanostatic control. Ionically blocking electrodes are used to probe the conductivity under opposite polarities to reveal possible differences in the defect structure across a thin film of CeO2. Data suggests the existence of a large spatial inhomogeneity that could give rise to constant phase elements during standard electrochemical characterization, potentially affecting the overall conductivity of films on the macroscale. The approach discussed here can also be utilized for other mixed ionic electronic conductor (MIEC) systems including memristors and electroresistors, as well as physical systems such as ferroelectric tunneling barriers.