Interferometric telescopes made of close-packed antenna elements are an important tool for imaging extended radio sources, specifically structures that have angular sizes comparable to or even greater than the FWHM of the beams of the antennas. They have proved useful in observations of cosmic microwave background anisotropies that require high brightness-sensitivity. However, the visibilities ...

A pointed endofunctor (and in particular a reflector) (R, r) in a category X is direct iff for each morphism f : X→ Y the pullback of Rf against rY exists and the unique fill-in morphism u from X to the pullback is such that Ru is an isomorphism. (This is close to the concept of a simple reflector introduced by Cassidy, Hébert and Kelly in 1985.) We give sufficient conditions for directness, an...

The 2-D and 3-D neutronics models for 10 MW nuclear research reactor of MTR type have been developed and presented in this paper. Our results agree very well with the results of seven countries mentioned in the IAEA-TECDOC233. To study the effect of reflector types on the reactor effective multiplication factor, five types of reflectors such as pure beryllium, beryllium, heavy water, carbon and...

The submillimeter antennas of the Atacama Large Millimeter Array (ALMA) have specifications that are beyond the current state of the art in accurate reflector antenna technology. Considering that as many as 64 of these antennas would eventually be needed, the ALMA partners AUI/NRAO and ESO each agreed to acquire a prototype antenna, and subject these to an extensive evaluation program. In this ...

Background: The scattering of Hand E-polarized plane waves by a two-dimensional (2-D) parabolic reflector made of graphene and placed in the free space is studied numerically. Methods: To obtain accurate results we use the Method of Analytical Regularization. Results: The total scattering cross-section and the absorption cross-section are computed, together with the field magnitude in the geome...

In this research work 2-D CPC (Compound Parabolic Concentrator) with flat plate absorber and two parabolic reflectors is first designed and then fabricated for thermal performance analysis. Here the incident rays, after reflection from the reflector, are not focused at a point but are simply collected on a line of absorber surface. Acrylic sheets are provided to reduce the heat loss. Flat plate...

We consider here antemas that could be usefid as part of a fize radar for penetrating munitions. The concept requires radiating an ultra-short pulse using an antenna with maximum gain and a compact design. Both lens and reflector Impulse Radiating Antennas (IRAs) are recommended as suitable candidates for this purpose. We summarize the properties of these antennas, and we describe two measureme...

One important parameter for an ultrasonic transducer is the echo it yields from a pointlike reflector. It can be measured directly but there are however certain problems connected with this. This reflector must have such a size that it can be considered a point, which results in a very weak echo and consequently a low SNR. We propose an alternative method to calculate the echo from a pointlike ...