Design of acoustic beam aperture modifier using gradient-index phononic crystals

This article reports the design concept of a novel acoustic beam aperture modifier using butt-jointed gradient-index phononic crystals (GRIN PCs) consisting of steel cylinders embedded in a homogeneous epoxy background. By gradually tuning the period of a GRIN PC, the propagating direction of acoustic waves can be continuously bent to follow a sinusoidal trajectory in the structure. The aperture of an acoustic beam can therefore be shrunk or expanded through change of the gradient refractive index profiles of the butt-jointed GRIN PCs. Our computational results elucidate the effectiveness of the proposed acoustic beam aperture modifier. Such an acoustic device can be fabricated through a simple process and will be valuable in applications, such as biomedical imaging and surgery, nondestructive evaluation, communication, and acoustic absorbers.     

Dauerhaftigkeit und mechanische Stabilität von Terrassendielen bei erhöhter Temperatur – Ein Werkstoffvergleich: WPC,thermisch modifiziertes Holz und Massivholz

This article deals with the differences in the long-term durability and thermal stability under load of terrace deckings from various materials. The tested materials were deckings made of wood, thermally modified timber (TMT), and wood–polymer–composites (WPC). For the determination of the test temperatures for component testing according to EN 310, the surface temperatures of the decks during a normal hot summer day were measured. A cyclic test according to EN 321 was applied to all decking materials. Afterwards the component testing was repeated. All wooden samples reveal considerable cracks, some were twisted, and few were even broken. In particular regarding the optical appearance, wood decks show advantages against the TMT decks. Some WPC decks show very fine cracks on the face, which were additionally analyzed by means of X-ray computed tomography (CT). Except for the WPC deck with higher wood content, no WPC deck revealed significant changes after the cyclic test. The CT analysis was also suitable to find cracks inside the materials and illustrate them. Thus, the whole damage inside a sample could be characterized by calculating a kind of error pattern. No considerable cracks or failures could be observed on the WPC decks.     

Anonymous attestation with user-controlled linkability

This paper is motivated by the observation that existing security models for direct anonymous attestation (DAA) have problems to the extent that insecure protocols may be deemed secure when analysed under these models. This is particularly disturbing as DAA is one of the few complex cryptographic protocols resulting from recent theoretical advances actually deployed in real life. Moreover, standardization bodies are currently looking into designing the next generation of such protocols. Our first contribution is to identify issues in existing models for DAA and explain how these errors allow for proving security of insecure protocols. These issues are exhibited in all deployed and proposed DAA protocols (although they can often be easily fixed). Our second contribution is a new security model for a class of “pre-DAA scheme”, that is, DAA schemes where the computation on the user side takes place entirely on the trusted platform. Our model captures more accurately than any previous model the security properties demanded from DAA by the trusted computing group (TCG), the group that maintains the DAA standard. Extending the model from pre-DAA to full DAA is only a matter of refining the trust models on the parties involved. Finally, we present a generic construction of a DAA protocol from new building blocks tailored for anonymous attestation. Some of them are new variations on established ideas and may be of independent interest. We give instantiations for these building blocks that yield a DAA scheme more efficient than the one currently deployed, and as efficient as the one about to be standardized by the TCG which has no valid security proof.     

A socially aware caching mechanism for encounter networks

Managing community content in mobile communities is challenging, since informal groups may emerge spontaneously whenever opportunities exist. To deal with group dynamics, encounter based community support systems can be a solution. In encounter networks, peers exchange content whenever they physically meet, i.e., whenever peers are near to each other. To assure content availability within the community network, content needs to be replicated (cached) and continuously updated. A?well known drawback of this scheme is the fact that the resource usage can be quite high. In this paper we present new caching strategies based on sociological knowledge, aiming at improving the overall content quality. We derive mobility and connectivity aware cache policies and simulate their benefit for knowledge building with urban life simulations. Results show that context precision and recall can be greatly improved in comparison to traditional cache strategies applied in the majority of encounter networks.     

Domestic demand-side response with heat pumps: controls and tariffs

ABSTRACT

Electric heat pumps feature prominently in projected energy transitions in the UK and elsewhere. Owing to their high electricity consumption, heat pumps are viewed as important targets for demand-side response (DSR). Findings are presented from a field trial of a new control system that aims to optimize heat pump performance, including under time-varying tariff conditions. The trial involved monitoring 76 properties with heat pumps, but without dedicated heat storage; 31 of these received the control system. Interviews were conducted with a subsample of 12 participants. The controller successfully evened out electricity demand over the day (reducing the evening peak), but this was associated with increased late night and daytime temperatures. Interview participants reported some disturbance owing to overnight heating and noise, as well as usability issues with the controller interface and hardware. These issues present risks to the future acceptability of such systems. While the system delivered short-term demand reductions successfully, longer-term demand shifting risked causing unacceptable disturbance to occupants. Future control systems could overcome some of the issues identified in this pioneering trial through more effective zoning, using temperature caps or installing dedicated heat storage, but these may either limit the available flexibility or be challenging to achieve.     

BioPACE

While developing the specifications for electronically enabled Machine Readable Travel Documents, the ICAO paid significant attention to security aspects related to the digital information stored in this type of electronic document. This has resulted in Passive and Active Authentication, Basic Access Control and Extended Access Control. The goal of Basic Access Control (BAC) is preventing unauthorized access to the chip data stored on eMRTDs. The PACE protocol has been developed as a future-proof method to overcome the limitations of BAC and to replace BAC in the future. In this paper the BioPACE protocol is proposed as a supplement to the PACE protocol. Besides verifying if the document holder is indeed the rightful owner, the BioPACE protocol provides a higher convenience for the bearer of the document.     

Solar water splitting with p-SiC film on p-Si: Photoelectrochemical behavior and XPS characterization

The electrochemical properties of single-crystalline p-type 3C-SiC films on p-Si substrate were investigated as an electrode in H₂SO₄ aqueous solutions in dark and under white light illumination. The photoelectrochemical (PEC) measurements indicates the p-type 3C-SiC film on p-Si substrate can generate a cathodic photocurrent as a photocathode, which corresponds to hydrogen production, and generate an anodic photocurrent as a photoanode, which corresponds to oxygen evolution. The surface chemical states of the films were investigated by XPS. In order to observe the surface chemical state changes after PEC test, the range of applied potential to the electrode was divided into three zones: −3.6 to 0 V, 0–1.5 V and 1.5–4 V vs. Ag/AgCl. After separated PEC tests in these three areas, XPS shows the surface of the SiC film in the range of −3.6 to 0 V and 0–1.5 V was stable without oxidation except the band bending occurred. But in the range of 1.5–4 V the film surface was oxidized due to anodic oxidation.     

Flammability of layered silicate epoxy nanocomposites combined with low‐melting inorganic ceepree glass

Tetraphenylphosphonium modified layered silicate epoxy nanocomposite (EP/TPPMMT) combined with low‐melting silicate glass, Ceepree (CP) is investigated by thermal analysis, flammability tests and cone calorimeter at different heat fluxes. Adding CP and TPPMMT does not change the pyrolysis apart from increasing inorganic residue. The total heat evolved (THE) is changed insignificantly, as neither relevant additional carbonaceous charring nor flame inhibition occurs. However, flame retardancy is clearly observed due to an inorganic‐carbonaceous surface protection layer. The peak heat released rate (PHRR) is reduced by around 32–42% when 5 wt% TPPMMT is added, and 51–63% when 10 wt% CP is added. PHRR reduction less than expected is observed when both additives are combined. The reduction is greater than that achieved by using TPPMMT but less than when only CP is used. The morphology of fire residue is investigated by scanning electron microscope on different length scales and turns out to be the key to understanding the efficiency of flame retardancy. The fire residue of EP/CP shows a layered structure, whereas separated columns limit the barrier properties for EP/5%TPPMMT on the micrometer scale. Columns dominating the fire residue structure of EP/5%TPPMMT/10%CP deteriorate the fire retardancy, whereas a more integral structure at the top of the residue causes the improvement over EP/5%TPPMMT. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers