A DC-coupled RF Amplifier in CMOS with DC-feedback

A CMOS multistage RF amplifier with DC coupling is presented. A complete optimisation of the various stages is done to maximize the RF gain for a given power budget. To decrease the effects of offsets and tolerances in high gain multistage amplifiers usually (lossy) AC coupling is used. The presented circuit employs DC coupling and DC control circuitry to avoid coupling-induced\ud losses. Compared to existing competing AC-coupled designs the presented one has much more gain at the same power consumption with a lower die area. For the 3-stage design vehicle, with Rsrc = 500Ω and Cout = 400fF, the maximal signal power gain at 4mA supply current is 33dB at 1.9GHz

Grid application meta-repository system

As one of the most popular forms of distributed computing technology, Grid brings together different scientific communities that are able to deploy, access, and run complex applications with the help of the enormous computational and storage power offered by the Grid infrastructure. However as the number of Grid applications has been growing steadily in recent years, they are now stored on a multitude of different repositories, which remain specific to each Grid. At the time this research was carried out there were no two well-known Grid application repositories sharing the same structure, same implementation, same access technology and methods, same communication protocols, same security system or same application description language used for application descriptions. This remained a great limitation for Grid users, who were bound to work on only one specific repository, and also presented a significant limitation in terms of interoperability and inter-repository access. The research presented in this thesis provides a solution to this problem, as well as to several other related issues that have been identified while investigating these areas of Grid. Following a comprehensive review of existing Grid repository capabilities, I defined the main challenges that need to be addressed in order to make Grid repositories more versatile and I proposed a solution that addresses these challenges. To this end, I designed a new Grid repository (GAMRS – Grid Application Meta-Repository System), which includes a novel model and architecture, an improved application description language and a matchmaking system. After implementing and testing this solution, I have proved that GAMRS marks an improvement in Grid repository systems. Its new features allow for the inter-connection of different Grid repositories; make applications stored on these repositories visible on the web; allow for the discovery of similar or identical applications stored in different Grid repositories; permit the exchange and re-usage of application and applicationrelated objects between different repositories; and extend the use of applications stored on Grid repositories to other distributed environments, such as virtualized cluster-on-demand and cloud computing

The large-scale jet-powered radio nebula of Circinus X-1

We present multi-epoch observations of the radio nebula around the neutron star X-ray binary Circinus X-1 made at 1.4 and 2.5 GHz with the Australia Telescope Compact Array between October 2000 and September 2004. The nebula can be seen as a result of the interaction between the jet from the system and the interstellar medium and it is likely that we are actually looking toward the central X-ray binary system through the jet-powered radio lobe. The study of the nebula thus offers a unique opportunity to estimate for the first time using calorimetry the energetics of a jet from an object clearly identified as a neutron star. An extensive discussion on the energetics of the complex is presented: a first approach is based on the minimum energy estimation, while a second one employs a self-similar model of the interaction between the jets and the surrounding medium. The results suggest an age for the nebula of \leq 10^5 years and a corresponding time-averaged jet power \geq 10^{35} erg s^{-1}. During periodic flaring episodes, the instantaneous jet power may reach values of similar magnitude to the X-ray luminosity.Comment: Accepted to MNRA

The first resolved imaging of milliarcsecond-scale jets in Circinus X-1

We present the first resolved imaging of the milliarcsecond-scale jets in the neutron star X-ray binary Circinus X-1, made using the Australian Long Baseline Array. The angular extent of the resolved jets is ~20 milliarcseconds, corresponding to a physical scale of ~150 au at the assumed distance of 7.8 kpc. The jet position angle is relatively consistent with previous arcsecond-scale imaging with the Australia Telescope Compact Array. The radio emission is symmetric about the peak, and is unresolved along the minor axis, constraining the opening angle to be less than 20 degrees. We observe evidence for outward motion of the components between the two halves of the observation. Constraints on the proper motion of the radio-emitting components suggest that they are only mildly relativistic, although we cannot definitively rule out the presence of the unseen, ultra-relativistic (Lorentz factor >15) flow previously inferred to exist in this system.Comment: Accepted for publication in MNRAS Letters. 6 pages, 4 figure

An outburst of SS 433 observed on milliarcsecond scale

SS 433 is a high-mass X-ray binary system (XRB) and one of the most persistent sources of relativistic jets in the Milky Way. The object has been intensively studied in radio at arcsecond scales, however the high-resolution observations (i.e. VLBI) are relatively scarce. In 2008 November the system was in outburst. Using the e-VLBI capabilities of the European VLBI Network (EVN) we observed SS 433 for three epochs during the active phase. The data offered a detailed view of the system’s behaviour in outburst at milliarcsecond scales. We used the “kinematic model" (which predicts the position along the jet of any knot ejected at some particular time in the past) to investigate the dynamic parameters of SS 433 and we examined the polarization properties of the ejected material. We report here the preliminary results