Definition, analysis and development of an optical data distribution network for integrated avionics and control systems. Part 2: Component development and system integration

Fiber optic transmission is emerging as an attractive concept in data distribution onboard civil aircraft. Development of an Optical Data Distribution Network for Integrated Avionics and Control Systems for commercial aircraft will provide a data distribution network that gives freedom from EMI-RFI and ground loop problems, eliminates crosstalk and short circuits, provides protection and immunity from lightning induced transients and give a large bandwidth data transmission capability. In addition there is a potential for significantly reducing the weight and increasing the reliability over conventional data distribution networks. Wavelength Division Multiplexing (WDM) is a candidate method for data communication between the various avionic subsystems. With WDM all systems could conceptually communicate with each other without time sharing and requiring complicated coding schemes for each computer and subsystem to recognize a message. However, the state of the art of optical technology limits the application of fiber optics in advanced integrated avionics and control systems. Therefore, it is necessary to address the architecture for a fiber optics data distribution system for integrated avionics and control systems as well as develop prototype components and systems

Room-temperature operation of GaAs Bragg-mirror lasers

Room-temperature operation of GaAs distributed Bragg reflector lasers is reported. The diodes are fabricated from conventional double heterostructures involving only a single step of liquid-phase epitaxy. For gratings with a period of 3700 Å, the diodes lased at 8770 Å, which corresponds to the high-absorption side of the spontaneous emission spectrum. Thresholds as low as 6 kA/cm^2 have been realized

Optically pumped GaAs surface laser with corrugation feedback

A GaAs distributed-feedback laser was fabricated and pumped optically. A narrow stimulated spectrum was obtained around 0.83 µ with threshold pumping power of ~2 × 10^5 W/cm^2

GaAs-GaAlAs distributed-feedback diode lasers with separate optical and carrier confinement

Remarkable reduction of the threshold current density is achieved in GaAs-GaAlAs distributed-feedback diode lasers by adopting a separate-confinement heterostructure. The diodes are lased successfully at temperatures up to 340 °K under pulsed operation. The lowest threshold current density is 3 kA/cm^2 at 300 °K

Liquid phase epitaxy of GaAlAs on GaAs substrates with fine surface corrugations

Liquid phase epitaxy of GaAlAs was performed on GaAs fine surface corrugations. By optimizing the growth conditions, GaAlAs layers were grown successfully with only minimal meltback

Plans for phase coherent long baseline interferometry for geophysical applications using the Anik-B communications satellite

A pilot project to establish an operational phase stable very long baseline interferometer (VLBI) for geophysical studies is described. Methods for implementation as well as practical applications are presented

Second Cluster Integral and Excluded Volume Effects for the Pion Gas

The quantum mechanical formula for Mayer's second cluster integral for the gas of relativistic particles with hard-core interaction is derived. The proper pion volume calculated with quantum mechanical formula is found to be an order of magnitude larger than its classical evaluation. The second cluster integral for the pion gas is calculated in quantum mechanical approach with account for both attractive and hard-core repulsive interactions. It is shown that, in the second cluster approximation, the repulsive pion-pion-interactions as well as the finite width of resonances give important but almost canceling contributions. In contrast, an appreciable deviation from the ideal gas of pions and pion resonances is observed beyond the second cluster approximation in the framework of the Van der Waals excluded-volume model.Comment: 29 pages, Latex, 9 PS-figure

Silicate features in the circumstellar envelopes of the Class~I binary driving source of HH250

We investigate the silicate feature of the two Class I components of HH250-IRS, a resolved binary system with a separation of $0''53$ driving a Herbig-Haro flow. Each component has its own circumstellar envelope, and the system is surrounded by a circumbinary disk. We have carried out low resolution spectroscopy in the 8-13$\mu$m range using VISIR at ESO's Very Large Telescope. The silicate features of both sources are clearly different. The NW component has a broad, smooth absorption profile lacking structure. The SE component shows the silicate feature in emission, with structure longwards of 9.5$\mu$m indicating the presence of crystalline dust in the dominant form of forsterite. The apparent lack of an absorption feature caused by foreground dust is probably due to the filling of the band with emission by amorphous silicates in the envelope of the object. Despite their virtually certain coevality, the differences in the components of the HH250-IRS binary are most likely due to markedly different circumstellar environments. The NW component displays an unevolved envelope, whereas dust growth and crystallization has taken place in the SE component. The weak or absent signatures of enstatite in the latter are fairly unusual among envelopes with crystalline dust, and we tentatively relate it to a possible wide gap or an inner truncation of the disk already hinted in previous observations by a drop in the $L'$-band flux, which might indicate that the SE component could actually be a very close binary. We speculate that the clear differences between the silicate feature spectra of both components of HH250-IRS may be due either to disk evolution sped up by multiplicity, or by accretion variability leading to episodes of crystal formation.Comment: Accepted by Astronomy and Astrophysic