AIDS: structure, replication and spread of the AIDS virus

AIDS (Acquired Immune Deficiency Syndrome)was first, described as a new disease of humans in 1981. The origins of the disease are controversial. AIDS is caused by a retrovirus, a type of virus which rarely attacks human cells. The first virus of this type recorded in humans is reponsible for a type of leukaemia and was identified in 1978. AIDS is thus the third type of human retrovirus to be discovered and hence, is referred to as T-lymphotrophic virus III (HTLV-III). For viruses to replicate, they have to invade a host cell which in this case is a T4-lymphocyte, a type of white blood cell that regulates the immune system. The problems of the disease result directly from the death of these cells. As a consequence, the immune system is compromised leading to a number of opportunistic secondary infections and other disorders.

Optical communications : past, present and future trends

In this talk we will review some of the key enabling technologies of optical communications and potential future bottlenecks. Single mode fibre (SMF) has long been the preferred waveguide for long distance communication. This is largely due to low loss, low cost and relative linearity over a wide bandwidth. As capacity demands have grown SMF has largely been able to keep pace with demand. Several groups have been identifying the possibility of exhausting the bandwidth provided by SMF [1,2,3]. This so called “capacity-crunch” has potentially vast economic and social consequences and will be discussed in detail. As demand grows optical power launched into the fibre has the potential to cause nonlinearities that can be detrimental to transmission. There has been considerable work done on identifying this nonlinear limit [4, 5] with a strong re- search interest currently on the topic of nonlinear compensation [6, 7]. Embracing and compensating for nonlinear transmission is one potential solution that may extend the lifetime of the current waveguide technology. However, at sufficiently high powers the waveguide will fail due to heat-induced mechanical failure. Moving forward it be- comes necessary to address the waveguide itself with several promising contenders discussed, including few-mode fibre and multi-core fibre.