Low noise amplication of an optically carried microwave signal: application to atom interferometry

In this paper, we report a new scheme to amplify a microwave signal carried on a laser light at $\lambda$=852nm. The amplification is done via a semiconductor tapered amplifier and this scheme is used to drive stimulated Raman transitions in an atom interferometer. Sideband generation in the amplifier, due to self-phase and amplitude modulation, is investigated and characterized. We also demonstrate that the amplifier does not induce any significant phase-noise on the beating signal. Finally, the degradation of the performances of the interferometer due to the amplification process is shown to be negligible

Performance of Multicast Packet Aggregation in All Optical Slotted Networks

The study focuses on packet aggregation mechanisms on the edge router of an optical network. The device works as an interface between the electronic and optical domains : it takes IP packets coming from client layers and converts them into optical packets to be sent into the optical network. An efficient aggregation mechanism supporting QoS (Quality of Service) requirements of IP flows is presented. A timer is implemented to limit the aggregation delay. Analytical models based on Markov chains are presented in order to study the packetisation efficiency (filling ratio) and the mean time of packetisation for each class. Numerical results show the effect of IP packet lengths distribution on aggregation delay and efficiency. Also, we show the importance of the timer in bounding the delay of transmitted packets without much altering the aggregation efficiency

State of nature

For the first time ever, the UK’s wildlife organisations have joined forces to undertake a health check of nature in the UK and its Overseas Territories. 60% of the 3,148 UK species we assessed have declined over the last 50 years and 31% have declined strongly. Half of the species assessed have shown strong changes in their numbers or range, indicating that recent environmental changes are having a dramatic impact on nature in the UK. Species with specific habitat requirements seem to be faring worse than generalist species. A new Watchlist Indicator, developed to measure how conservation priority species are faring, shows that their overall numbers have declined by 77% in the last 40 years, with little sign of recovery. Of more than 6,000 species that have been assessed using modern Red List criteria, more than one in 10 are thought to be under threat of extinction in the UK. Our assessment looks back over 50 years at most, yet there were large declines in the UK’s wildlife prior to this, linked to habitat loss. The UK’s Overseas Territories hold a wealth of wildlife of huge international importance and over 90 of these species are at high risk of global extinction. There is a lack of knowledge on the trends of most of the UK’s species. As a result, we can report quantitative trends for only 5% of the 59,000 or so terrestrial and freshwater species in the UK, and for very few of the 8,500 marine species. Much needs to be done to improve our knowledge. What we do know about the state of the UK’s nature is often based upon the efforts of thousands of dedicated volunteer enthusiasts who contribute their time and expertise to monitoring schemes and species recording. The threats to the UK’s wildlife are many and varied, the most severe acting either to destroy valuable habitat or degrade the quality and value of what remains. Climate change is having an increasing impact on nature in the UK. Rising average temperatures are known to be driving range expansion in some species, but evidence for harmful impacts is also mounting. The full report is online: www.rspb.org.uk/stateofnature We should act to save nature both for its intrinsic value and for the benefits it brings to us that are essential to our wellbeing and prosperity. Targeted conservation has produced inspiring success stories and, with sufficient determination, resources and public support, we can turn the fortunes of our wildlife around. The State of Nature report serves to illustrate that with shared resolve and commitment we can save nature