Abstract: A method of improving the security of computer communications over a connecting network comprising the steps, carried out before a data packet enters the connecting network from a user domain, of tagging the data packet from a user domain with a security level marking and appending the tagged data packet with a string formed from a check-sum made over the data packet and security level marking tag to form a datagram. The integrity of the data is protected and the method can be used to prevent the mis-routing of data packets to user domains of lower security classification.

Abstract: Described herein is a system for the management of security domains. The system comprises a managing security domain (10), a firewall (70) and two or more managed security domains (80, 100). The managing security domain (10) includes a plurality of nodes (12, 14, 16) of which one is a management node (16) for managing the domain (10). Each managed security domain (80, 100) comprises a plurality of nodes (82, 84, 102, 104). The management node (16) operates in conjunction with the firewall (70) to manage the managed domains, the firewall (70) allowing the transfer of information across domains having different security levels.

Abstract: A re-circulating amplifier comprising a SAW filter with group delay characteristics for providing a time delay function.

Abstract: The sensor has an outer member 10 formed with an upwardly directed hole 12 having an open upper end 14. An inner member in the form of a tube 16 is provided having a lower portion 18 positioned in the hole 12 and an upper portion 19 which projects above the outer member 10. Solar radiation applied to the upper portion 19 of the tube 16 creates a chimney effect which causes air to flow upwardly inside the tube 16 and downwardly from the open upper end 14 through a space 22 between the inner and outer members 10, 16. Sensing devices 24, 26 for sensing temperature and humidity are arranged within the outer member 10 and in the air flow path.

Abstract: In a radar system it is necessary to distinguish signals reflected from wanted targets such as aircraft from those reflected from fixed terrain features, known as clutter. The clutter signals can in some cases be significantly stronger than the wanted signals. One method for dealing with land clutter is the use of a high resolution clutter map. The area around the radar is considered to be divided into cells, and an array of background signal estimates is maintained for these cells. Whenever a signal is received by the radar, it is compared with the stored background level for the cell it occupies, and a detection is only reported if the signal exceeds the background by a pre-set threshold. Received signals are also used to modify the stored background levels so that the clutter map adapts to the reflections from clutter which are present over long periods. Clutter maps have so far only been used successfully for radars at fixed locations.