The stellar content of the Orion OB1 association

We present a photometric investigation, using the VBLUW system, of the stellar content of Orion OB1. Physical parameters (logg, logT _eff) for the stars are derived with the aid of model atmospheres. From these, visual extinctions, absolute magnitudes and distance moduli are derived. The distance moduli are used to determine membership for the stars in each of the subgroups and distances to the subgroups are calculated. The ages of the subgroups are derived through isochrone fitting and the IMF is derived for each subgroup. The energy deposited into the ISM through stellar winds and supernovae is calculated and compared to observed large scale features in the ISM around Orion OB1.     

MultiWaveLink: An interactive data base for the coordination of multiwavelength and multifacility observations

MultiWaveLink is an interactive, computerized data base that was developed to facilitate a multiwavelength approach to studying astrophysical sources. It can be used to access information about multiwavelength resources (observers, telescopes, data bases and analysis facilities) or to organize observing campaigns that require either many telescopes operating in different spectral regimes or a network of similar telescopes circumspanning the Earth.     

Doppler Processor Rejection of Range Ambiguous Clutter

Doppler processors are used in radar to separate target returns from clutter. When the clutter is at a range farther than the unambiguous range of the radar, the ability to reject the clutter is degraded. In this article the degradation is analyzed for an N-pulse batch processor with Dolph weighting, and the results show how degradation varies with design sidelobe level.     

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.     

Aerosols within the world climate research programme

Based on the findings of the meeting of JSC experts on “Aerosol and Climate” (Geneva, 27–31 October 1980) the general research strategy consisting of three phases will be presented. The three phases are: Phase I: Sensitivity tests with available models Phase II: Improvement of climate models and data bases Phase III: Development of advanced climate models with internal aerosol generation and regulation processes. COSPAR's role within this research strategy is outlined.     

Perturbation solutions for variable energy blast waves

The trajectory of and the flow field behind blast waves with time varying energy input is determined. Freeman's (1968) Lagrangean coordinate formulation is modified to include both the geometric factor, α, for plane, cylindrical and spherical shocks and also non-integer values of β, the energy input parameter, in a single computational algorithm. Numerical problems associated with vanishing density at the inner mass boundary or “piston face” are then examined and solved. Second order perturbation solutions about the solution for an infinite strength shock are then obtained in Sakurai's (1965) inverse shock Mach number expansion parameter for 0 β < α + 1. Tables and graphs of significant numerical coefficients are presented for comparison to, and extension of, results of other authors. Graphs of typical shock trajectories and flow field density, pressure and velocity variations are also presented and discussed.     

Stigmatic bragg crystal spectrometers for cosmic X-rays

Two instruments, one a large free-standing self-focusing spherical array and the other a small cylindrical crystal used at the focus of a large grazing incidence x-ray collector, are discussed. Both instruments offer several advantages over more conventional spectrometers, i.e., mechanical simplicity, moderate resolving power (10²), and good sensitivity.     

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.     

Spectral Analysis and Subtraction of Noise in Radar Signals

A new method of maximum entropy spectral estimation called the revised maximum entropy method (MEM) is formulated and is applied to the spectral analysis of the echo signals from atmospheric turbulence observed by an incoherent scatter radar. The revised MEM is shown free from many demerits of the other methods for spectral analysis. Further it makes it possible to subtract the white noise usually contained in the data during the processing. Some examples of spectral estimation are shown for the actual radar signals and the simulated data. Another application of the revised MEM is the subtraction of the clutter component which is difficult to do by linear filtering. The method is successfully applied to several data abounding with the clutter to obtain the spectra of the echo signals with less clutter distortion.