Three ways to implement interfacial techniques: application tomeasurements of chromatic dispersion, birefringence, and nonlinearsusceptibilities

Depending on the spectal width of the source illuminating an interferometer, measurement procedures can utilize either the whole interferogram, or only the fringe envelope, or only the fringe quick oscillations. With an ultraband spectrum source, a simplified adaptation of the methods of Fourier transform spectroscopy yields the variations of the test-fiber propagation constant over the whole wavelength-interval of the source. Chromatic dispersion can then be computed from a single interferogram. With narrower spectrum sources, only the fringe envelopes are utilized and yield measurements of mode delay, with application to chromatic and polarization mode dispersion. In this case, however, interferograms at several wavelengths are necessary. With even narrower spectrum sources, the fringe quick oscillations provide measurements of phase shifts, related to changes in the mode propagation constant, when outside perturbations are applied to the test fiber. A direct method for measuring the third-order nonlinear susceptibilities is discussed. In this case the outside perturbation is an intense pump laser field     

Implementation of Quality Criteria in Tendering and Regulating Infrastructure Management Contracts

In recent years, several public authorities have been making advances in developing bidding terms for contracts regulating the management of infrastructure. Up to now these bidding terms have focused on granting the contract to the bidder who, having agreed to comply with the requirement of a specified level of quality, as stipulated in the contract, submits the lowest tender in terms of price. As a result, the experience of implementing quality-related incentives for the management of infrastructure has been scarce. This paper demonstrates that, if infrastructure quality is verifiable and the social benefit derived from it is measurable, there is a better way both to tender and to regulate those contracts, based on a combination of price and quality standards. In addition, the paper proposes a new procurement procedure to encourage bidders to provide better quality levels. The last part of the paper provides a practical example of how to calculate a quality index for contracts regulating the management of infrastructure. The paper ends with a set of conclusions related to the advantages of the new tendering mechanism and its possible application.     

PN Regenerative Ranging and Its Compatibility With Telecommand and Telemetry Signals

This paper investigates the performance of a satellite communication system which the onboard receiver regenerates the uplink pseudonoise (PN) ranging sequence. Using phase modulation, the PN ranging signal is transmitted together with the telecommand signal in the uplink and the telemetry signal in the downlink. Various ranging sequences are taken into consideration and tested prior to final international adoption. The reciprocal interference among telemetry, telecommand, and ranging signals is evaluated in terms of bit error rate and ranging phase acquisition time.     

The European Space Agency's Deep-Space Antennas

The European Space Agency (ESA) is today autonomously flying three interplanetary missions: Rosetta traveling to the comet Churyumov-Gerasimenko and the two orbiters Mars Express and Venus Express. The capability of supporting these and future deep-space missions is the consequence of a farsighted decision taken in 1996 to expand the ESA network of 15-m tracking antennas into the deep-space domain. The ambitious plan to provide around-the-clock coverage to all ESA interplanetary missions is almost completed: two deep-space antennas, located in New Norcia (Australia) and Cebreros (Spain), have been in operation since 2002 and 2005, respectively, while a third antenna is planned for 2011. This paper presents the two existing antennas starting from the underlying system requirements originated from the Rosetta mission, which was the most demanding in terms of required performance. The selected architecture is then described, followed by a detailed discussion about the critical performances that play a major role in deep-space support and the associated design issues.     

Estimating forage quantity and quality under different stress and senescent biomass conditions via spectral reflectance

Assessing forage quantity and quality through remote sensing can facilitate grassland and pasture management. However, the high spatial and temporal variability of canopy conditions may limit the predictive accuracy of models based on reflectance measurements. The objective of this work was to develop this type of models, and to challenge their capacity to predict plant properties under a wide range of environmental conditions. We manipulated Paspalum dilatatum canopies through different stress treatments (flooding, drought, nutrient availability, and control) and by artificially varying the amount of senescent biomass. We measured canopy reflectance and constructed simple models, based on either normalized vegetation indices or a few selected wavebands, to estimate biomass and two variables related to forage quality: proportion of photosynthetic vegetation and biomass C:N ratio. General models satisfactorily predicted plant properties for the whole set of environmental conditions, but failed under specific conditions such as drought (for estimates of plant biomass), fertilization (for estimates of C:N ratio), and different levels of senescent tillers (for estimates of the proportion of photosynthetic vegetation). Where general models failed, specific models, based on different bands, achieved satisfactory accuracy. The general models performed better when based on a few selected bands than when based on two-band vegetation indices, having better accuracy (higher R²) and parsimony (lower BIC). However specific models performed similarly for both approaches (similar R² and BIC). These results indicate that these plant properties can be predicted from reflectance information under a broad range of conditions, but not for some particular conditions, where ancillary data or more complex models are probably needed to increase predictive accuracy.     

Rigorous and approximate calculations of antireflection layer parameters for travelling-wave diode laser amplifiers

An integral equation method is used for an accurate numerical analysis of antireflection layers for travelling-wave diode laser amplifiers. Its results are compared with those of various approximate analyses; a new practical approximation is proposed.