Transformation of a delta: Converting estuaries to lakes

In this century large-scale transformations have been carried out in the delta of the Rhine, Meuse and Scheldt in The Netherlands. The following principal consequences are considered: the loss of estuarine ecosystems, the change in the process of sedimentation and erosion, and the development of new aquatic and terrestrial ecosystems. The ecological consequences of the transformation of the Grevelingen estuary into a salt-water lake and some surprising developments are described briefly. The need for a limited restoration of the water exchange between the lake and the North Sea is indicated, as well as the major impacts of the exchange. The necessity for the maintenance or restoration of estuaries, the ecological development and the possibilities of the new lakes, and the management of these lakes by engineering structures are discussed. Careful land-use planning and ecosystem management, backed by research, are needed to make the fullest possible use of the potential offered by new lakes. It is also concluded that salt lakes have interesting perspectives.     

Attitude and Oribit Estimation Using Stars and Landmarks

An extended Kalman filter is used to process line-of-sight measurements to stars and known landmarks providing a statistical indication of performance in estimating spacecraft attitude, orbital ephemeris, and the bias drift of a set of three strapdown gyros. The landmark measurements were assumed to have been taken from the imagery of an Earth-observing multispectral scanner. It is shown that filtering of these noisy measurements results in highly accurate estimates of the above parameters. Results are given showing the sensitivity of performance to various system parameters such as star tracker accuracy, errors in the knowledge of landmark position, and number of stars and landmarks processed.     

The structural features of the germanium-silicon solid solution crystals obtained under microgravity

Structural features of germanium-silicon solid solution crystals have been investigated and silicon distribution in the crystals has been studied. All the crystals obtained under microgravity had, in spite of good external shape and facetting, a poorer internal structure than those obtained on Earth. The distribution of silicon have been shown to be non-uniform. High dislocation densities were observed.     

Probability of Anomaly Expressions for Random Waveform Registration

Registration by integral-square error correlation of one-dimensional discrete-time waveforms which are treated as random processes with specified autocorrelation functions is considered. An important design parameter for this class of problems is the probability of anomaly (a false dip in the correlation function) because it gives an indication of system immunity to gross registration errors. Explicit expressions for this parameter are not possible, so bounds and appoximations must be derived. Two upper bounds and an approximation for the probability of anomaly are derived here. The use of these expressions is illustrated by an example. The relative utility of these performance indicators is shown for the example by comparison with actual values of the probability of anomaly obtained by computer simulation.     

Enhanced resolution in simple radars

Many simple radars use fact-risetime pulses, but wide bandwidth does not translate into corresponding high resolution since the spectrum is far from flat. A scheme for enhancing down- and cross-range resolution of multiple targets through a two-step partial equalization of the spectrum is illustrated by detailed computer simulation, with emphasis on the tradeoffs between resolution and signal-to-noise ratios. Three examples are treated: two equal scattering centers, two unequal scattering centers, and compound target     

Sensor compensation for vehicle magnetic signatures

Most land vehicles whose positions need to be tracked are made primary of steel. The problem considered is that of finding locations within or on land vehicles where magnetic sensors can be mounted to measure heading accurately and of finding compensation methods that minimize the effect of the vehicle magnetic signature. Results obtained with various types of vehicles in several world locations are given. Advantages and disadvantages of pendulous mounting are considered, and vehicle magnetic changes caused by driving in areas of extremely strong magnetic fields such as those generated by DC-powered trains are discussed     

MARC-a system for simulation and visualization of space missionscenarios

MARC (modeling, animation, rendering, and compositing), a system using advanced computer graphics and animation techniques for spacecraft mission simulation, is described. The MARC system provides capabilities for generating complex models of both man-made and natural phenomena. The system models orbital dynamics of terrestrial satellites, supports solid models for the Earth, Sun, and Moon, and simulates the dynamics of terrestrial satellites for arbitrary elliptical orbits. A stellar background including magnitudes and spectral types is generated. The elements of the MARC system, including object modeling tools, orbital animation techniques, the rendering system used to compute individual frames, and the compositing techniques used, are discussed. The software architecture of the MARC system and the hardware used to support the system are described     

Lyapunov stability designs for switching regulator/low-pass filtersystem

The second method of Lyapunov is employed to determine quantitatively accurate criteria for asymptotic stability of the fourth-order switching-regulator/low-pass filter system. Modeling the regulator as a linearized negative resistance, this analysis provides alternative stability relationships to those found in the literature and also reveals the limitations of the Routh stability criterion. Design examples are included which ensure system stability and reduce the amplitude of the filter resonant peak (audio-susceptibility constraint)     

Simulation of DC spacecraft power systems

A modular state-variable approach is presented for DC spacecraft power system modeling and simulation. Each modular component is treated as a multiport network, and a state model is written with the port voltages as the inputs. The state model of a component is solved independently of the other components, using its state transition matrix. The state variables of each component are updated, assuming that the inputs are constant. Network analysis principles are then utilized to calculate the component inputs     

Highly variable X-ray emitting objects in the Rho Oph dark cloud

The Rho Ophiuchi dark cloud region has been the subject of an extensive guest investigation using the $\text{Einstein}$ Observatory. The set of observations comprise 14 IPC fields and 3 HRI fields. The densest part of the cloud has been observed 6 times. Forty seven sources were detected at a level > 3.5 σ and twenty more above 2 σ. The majority of these sources have optical, IR, or even radio continuum counterparts; nine are identified with known T Tauri stars, while several others are identified with stars showing H α in emission. All show a high degree of time variability; flux variations reach factors of 5 in a few hours, or 25 in a day. Apparent luminosities are in the range 10(30) – 10(31)(1) erg.s^?1. The possibility that the X-ray variability is due to flares is examined. If this interpretation is correct, one source has been the seat of the largest stellar flare ever recorded in X rays [L_x = 10(32) erg.s^?1, E_x ?10(36) ergs^-].