Efficient approximation to calculate time delay and dispersion in linearly chirped periodical microphotonic structures

The Bloch mode propagation through the chirped periodical structure is defined by its local dispersion relation. In a slowly varying structure its time delay is the integral of the local inverse group velocity along the propagation direction. The integration can be strongly simplified for linearly chirped structures if the assumption is made that the local dispersion relation is just a scaled and shifted version of the dispersion relation at the input. This assumption leads to exact solutions for the structures with locally uniaxial deformation and provides a good approximation for arbitrary structures with small chirps. The approach is demonstrated for high index contrast chirped Bragg mirrors and complicated photonic crystal waveguide structures, including coupled waveguides and a slow group velocity waveguide.     

Development of a new combined corrosion protection system for chloride‐contaminated reinforced concrete structures

Chloride‐induced damage of reinforcing steel is especially for parking garages and bridges often very severe as large amounts of chlorides act on horizontal surfaces which could lead to fast ingress of these detrimental ions up to the level of the reinforcement and subsequently to high rates of corrosion. In order to avoid the disadvantages of conventional rehabilitation (unreliable prognosis with patch repair or high costs and regular maintenance with cathodic protection using impressed current) a new combined protection system was developed where the principle of drying out the concrete (by means of a surface protection system) is combined with a temporary cathodic protection (by means of a sprayed zinc layer) during the transitional period of the drying out process. This new system was tested both in the laboratory and on‐site at a pilot application. Based on the results obtained the possibilities and limitations of the new system are discussed in this paper.     

Failure of Emergency Batteries for Aircrafts due to Stress-Corrosion Cracking

Several electrical brass (CuZn37) connector bolts of aircraft batteries failed as a result of stress-corrosion cracking. The batteries are used for emergency supply of the avionics in case of power failure or for complete control in the case of engine failure. For activation, the thermal battery is heated by a pyrotechnic element and then supplies electrical power with 5 A for 20 min up to 240 A for 3 min. For assembly of the batteries, an acetic acid curing silicone resin is used for housing seal on the lid and on the connector bolts. Because of the almost hermetic sealing of the enclosure, the silicone resin cures very slowly and metallic parts are exposed to the acetic acid vapor. So the electrical brass connector showed corrosive attack with the formation of copper acetate (verdigris). Subsequent failure due to stress-corrosion cracking occurred. The failure type and damage mechanisms could be simulated in laboratory experiments.     

Erosion Corrosion on Oil Coolers for Navy Ships

Incorrect material selection does not always lead to corrosion. In addition to an inferior selection of materials, unsuitable operating conditions and poor design also contributed to the presented failure. A combination of erosion and corrosion caused a leak in an oil cooler of a Navy ship. Because there was no welding seam between the deflectors and tube plate on the carbon steel cooler, cooling water could stream between them, and the flow rate became excessive. This caused erosion on the tube plate. In addition, the repeated change of the cooling liquid after servicing caused a uniform corrosion attack.     

A monolithic PDMS waveguide system fabricated using soft-lithography techniques

A monolithic waveguide system using poly(dimethyl siloxane) (PDMS) was designed, fabricated, and characterized. The waveguide demonstrated good confinement of light and relatively low attenuation at 0.40 dB/cm. The robustness and handling properties of the completed waveguides were excellent, and the process yield exceeded 96%. The waveguide did exhibit moderate temperature and humidity sensitivity but no temporal variation, and insertion loss remained stable over extended periods of time. Applications of this waveguide system in microscale sensing are immense, judging by the frequency of use of PDMS as the substrate for microfluidic and biomedical systems. The monolithic nature of the waveguides also reduces their cost and allows integration of optical pathways into existing PDMS-based microsystems.     

Mood dependent memory for internal versus external events.

Events that originate through internal mental operations such as reasoning, imagination, and thought may be more colored by or connected to one's current mood than are those that emanate from external sources. If so, then a shift in mood state, between the occasions of event encoding and event retrieval, should have a greater adverse impact on one's memory for internal than for external events. To investigate this inference, a series of studies was conducted that relied on a continuous music technique to modify mood, and on the generate/read procedures devised by N. J. Slamecka and P. Graf (see record 1980-20399-001) to distinguish internal from external events. Considered collectively, the results suggest that internal events are less likely than external events to be recalled after a shift in mood state. Discussion centers on both the empirical limitations and theoretical implications of the present result, as well as on prospects for future research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Short-Wave Infrared HgCdTe Electron Avalanche Photodiodes for Gated Viewing

Short-wave infrared (SWIR) HgCdTe electron avalanche photodiodes (eAPDs) with different doping profiles have been characterized for use in SWIR gated viewing systems. Gated viewing offers enhanced image contrast in scenes with clutter from the foreground or background. HgCdTe-based eAPDs show exponential gain–voltage characteristics and low excess noise and are, therefore, well suited for active imaging applications. The gain achievable at a fixed reverse voltage varies with the bandgap of the Hg_1?xCd_xTe detector material. We analyze current–voltage and gain–voltage plots measured on SWIR Hg_1?xCd_xTe eAPDs with x?=?0.45, corresponding to a cutoff wavelength of 2.55 μm at 150 K. The cutoff has been chosen as a trade-off between achievable APD gain and operating temperature for SWIR gated-viewing systems with target distances of about 1000 m. Focal plane arrays with a readout-integrated circuit featuring a fast internal clock have been built and their performance with respect to gated viewing applications has been evaluated on a laboratory demonstrator for short distances. Future plans for a field demonstrator for distances up to 1000 m are described briefly at the end.