Coherent optical receiver for 680 Mbit/s using phase diversity

A coherent optical receiver using a multiport optical coupler to provide phase diversity is described. By this means, only homodyne bandwidth is required in the signal processing, but with tolerances on the frequency tracking typical of heterodyne systems. Measured sensitivities with limited local-oscillator power are ?47.5 dBm at 320 Mbit/s and ?42 dBm at 680 Mbit/s. The results at the higher bit rate are strongly influenced by limited receiver module bandwidth.     

Improved theory for microstrip antennas

An improvement to a recently reported theory for the analysis of the pattern and impedance loci of microstrip antennas is developed. It yields a theory that is simple and inexpensive to apply. This is achieved by lumping all antenna losses into an effective dielectric loss tangent and then analysing the microstrip antenna as a lossy cavity. It is found that the resulting expression for impedance of the microstrip antenna is in good agreement with measured results for all modes and feed locations.     

Microstructural analysis of fusion and heat affected zones in electron beam welded ALLVAC 718PLUS™ superalloy

The fusion zone and heat affected zone (HAZ) microstructures of electron beam welded superalloy 718PLUS™ (718 Plus) that has been newly developed by ATI ALLVAC were examined. The microsegregation pattern during solidification of the fusion zone indicated that while Fe, Co, W, and Cr segregated to the core of the gamma dendrites, Nb, Ti, and Al were extensively rejected into the interdendritic liquid. Electron diffraction and X-ray microanalysis using transmission electron microscopy (TEM) of the fusion zone showed that the major secondary phases that formed from the interdendritic liquid were gamma/MC type carbide eutectic and gamma/Laves eutectic constituents. HAZ microstructure showed partially melted zone immediately adjacent to the fusion zone and intergranular microfissuring associated with resolidified products which suggested that HAZ cracking in this alloy occurred by liquation cracking. Microstructural examination of the HAZ using analytical scanning electron microscope showed resolidified gamma/Laves eutectic on the cracked and backfilled grain boundaries. Fine resolidified MC type carbide particles were also observed in the HAZ. Causes of grain boundary liquation were identified and the solidification of intergranular liquid in the HAZ was discussed.     

Fine-spray (water mist) protection of shipboard engine rooms

Twenty-three fire tests were conducted to determine the ability of current fine-spray (water mist) technologies to extinguish fires specified in the International Maritime Organization (IMO) fire test procedure for engine rooms greater than 3000 m³. The tests were conducted using nozzle installed at a 5 m height and 1·5 m spacing in a large test facility (2800 m² area and 18 m height). Two types of nozzles were tested: a low pressure nozzle operating between 1·2 and 1·5 MPa with flow per nozzle between 12·0 and 13·41/m and a multi-nozzle high-pressure prototype consisting of seven nozzles operating at 6·9 MPa flowing at 5·3 1/m per prototype. These nozzles were selected because they had been shown to extinguish IMO fire tests in enclosures with a protected area of 83 m² and a ceiling height of 4·5 m. The fire tests selected from the IMO procedure included 6 MW diesel spray fires on top of the IMO engine mock-up, a shielded 6 MW diesel spray fire adjacent to the mock-up, a 1 MW shielded diesel spray fire adjacent to the mock-up, and a wood crib within a 2 m² pan filled with heptane. In tests in which no additional enclosure surrounded the nozzles other than the test facility, fires were not significantly affected by the water mist using either nozzle. To further investigate mist-system capabilities, a ceiling was then placed directly over the nozzles at a 5 m height covering an area of 188 m². Using 90 high-pressure prototype nozzles, the test fires were not extinguished. A 940 m³ enclosure was then formed by dropping tarpaulins to the floor from the ceiling. A 4 m² vent was placed in the wall. With the 90 high-pressure prototype nozzles, the 6 MW spray fire on top of the mock-up was extinguished. When the 6 MW fire was shielded beside the mock-up, the fire was not extinguished. With the vent closed, the 6 MW shielded spray fire was extinguished. Under the same test conditions, a 1 MW shielded diesel spray fire and a 0·1 m² heptane pool fire were not extinguished. The fire test results indicated that protection of engine rooms with volumes of about 1000 m³ is possible by optimizing current fine-spray technology while significantly larger volumes will require improved discharge characteristics.     

Fire detection, location and heat release rate through inverse problem solution. Part II: Experiment

The design and fabrication of a prototype video fire detection system, which can locate a fire and determine its heat release rate, is described. The operation of the prototype system is demonstrated in a series of small-scale tests. The system utilizes a video camera to monitor an array of passive sensors distributed around the compartment to be protected. Each of the sensors is made up of a temperature-sensitive sheet that changes color at a prescribed temperature. In the event of an accidental fire, the plume of hot combustion gases rising from the fire will cause the temperature-sensitive sensors to be activated and change color. The times and locations of sensors changing color are used as data for an inverse problem solution algorithm, which determines the location and the heat release rate of the fire. A small-scale evaluation of the prototype video system is presented in which the prototype system is used to detect, locate and determine the heat release rate of a 2·4 kW burner placed in a 2·75 m wide by 2·75 m deep by 1·5 m high test enclosure. The accuracy of the prototype system in locating and determining the heat release rate of the small flame source placed in the reduced-scale enclosure is reported. In addition, the ability of the prototype system to make approximate measurements of the optical thickness of smoke in the enclosure, along camera-sensor lines-of-sight and then to use these measurements to locate and track the growth of a smoke plume is demonstrated.     

Internal pressure dynamics of a leaky building with a dominant opening

A simplified and computationally efficient model of internal pressure response of a building with a dominant opening and background leakage is presented based on certain simplifications shown to be adequate for all practical purposes. The presented model adequately linearized is used to develop closed form non-dimensional design solutions that can be used to estimate the ratio of internal to external pressure fluctuations and gust factors for a range of building volumes, opening sizes and porosity ratios. Experiments carried out with different combination of leakages in the presence of dominant openings of various sizes are used to justify the simplifications adopted in the derivation of the model and validate the model predictions. A performance analysis of the model carried out in conjunction with some approaches found in the literature on benchmarking data exhibits the relative advantage of the model in terms of accuracy, practical usage and computational expense.     

Simplified Models for Induction Machine Transients under Balanced and Unbalanced Conditions

Several simplified models of induction machines are presented. Included is a novel second-order model, which reduces the computational requirements previously considered necessary to predict electrical rotor transients, as well as mechanical transients. It is shown that the reduced-order models can be readily adapted to unbalanced voltage inputs without raising model order, thus providing increased flexibility. The model responses are compared for symmetrical voltage dips, start-up, and a sudden single-phasing condition.     

An anionically prepared flexible adhesive: 1: Synthesis

A method is described whereby epoxides based on a diglycidyl ether of bisphenol A (DGEBA) may be flexibilized by reaction with dienes such as butadiene or isoprene (M). The process requires the reaction of a tetrahydrofuran solution of DGEBA and diene with excess alkali metal, and the initial step is that of formation of diene dianion which homopropagates until terminated by DGEBA. The isolated product consists of a mixture of unreacted DGEBA and modified DGEBA. Preliminary tests indicate that this mixture exhibits adhesive properties superior to that of the original epoxide.