Nik Looker

MOAO first on-sky demonstration with CANARY

Context. A new challenging adaptive optics (AO) system, called multi-object adaptive optics (MOAO), has been successfully demonstrated on-sky for the first time at the 4.2 m William Herschel Telescope, Canary Islands, Spain, at the end of September 2010. Aims. This system, called CANARY, is aimed at demonstrating the feasibility of MOAO in preparation of a future multi-object near infra-red (IR) integral field unit spectrograph to equip extremely large telescopes for analysing the morphology and dynamics of high-z galaxies. Methods. CANARY compensates for the atmospheric turbulence with a deformable mirror driven in open-loop and controlled through a tomographic reconstruction by three widely separated off-axis natural guide star (NGS) wavefront sensors, which are in open loop too. We compared the performance of conventional closed-loop AO, MOAO, and ground-layer adaptive optics (GLAO) by analysing both IR images and simultaneous wave-front measurements. Results. In H-band, Strehl ratios of 0.20 are measured with MOAO while achieving 0.25 with closed-loop AO in fairly similar seeing conditions (r 0 ≈ 15 cm at 0.5 μm). As expected, MOAO has performed at an intermediate level between GLAO and closed-loop AO.

Increasing Web Service Dependability Through Consensus Voting

This paper demonstrates our Web Service based N-Version model, WS-FTM (Web Service-Fault Tolerance Mechanism), which applies this well proven technique to the domain of Web Services to increase system dependability. WS-FTM achieves transparent usage of replicated Web Services by use of a modified stub. The stub is created using tools included in WS-FTM. Our initial implementation includes a simple consensus voter that allows generic result comparison. Finally we show, through the use of a non-trivial example, that WS-FTM can be used to increase the reliability of a Web Service system.

WS-FIT: a tool for dependability analysis of Web services

This work provides an overview of fault injection techniques and their applicability to testing SOAP RPC based Web service systems. We also give a detailed example of the WS-FIT package and use it to detect a problem in a Web service based system.

Assessing the dependability of OGSA middleware by fault injection

This paper presents our research on devising a dependability assessment method for the upcoming OGSA 3.0 middleware using network level fault injection. We compare existing DCE middleware dependability testing research with the requirements of testing OGSA middleware and derive a new method and fault model. From this we have implemented an extendable fault injector framework and undertaken some proof of concept experiments with a simulated OGSA middleware system based around Apache SOAP and Apache Tomcat. We also present results from our initial experiments, which uncovered a discrepancy with our simulated OGSA system. We finally detail future research, including plans to adapt this fault injector framework from the stateless environment of a standard Web service to the stateful environment of an OGSA service.

A comparison of network level fault injection with code insertion

This paper describes our research into the application of fault injection to Simple Object Access Protocol (SOAP) based service oriented-architectures (SOA). We show that our previously devised WS-FIT method, when combined with parameter perturbation, gives comparable performance to code insertion techniques with the benefit that it is less invasive. Finally we demonstrate that this technique can be used to compliment certification testing of a production system by strategic instrumentation of selected servers in a system.

Determining the dependability of Service-Oriented Architectures

This paper introduces our novel method for the generation of fault injection test cases and failure detection by the use of our enhanced fault and failure models. Our enhanced fault model is an extension of a standard fault model that is constructed through decomposition to create a framework that facilitates automatic test generation. The failure model is based on a set of failure modes and again decomposed to create a framework to aid in the automatic detection of system failures. We demonstrate the Web Service-Fault Injection Technology (WS-FIT) method and fault injection tools with the use of some simulated real-world system.

Experience with wavefront sensor and deformable mirror interfaces for wide-field adaptive optics systems

Recent advances in adaptive optics (AO) have led to the implementation of wide field-of-view AO systems. A number of wide-field AO systems are also planned for the forthcoming Extremely Large Telescopes. Such systems have multiple wavefront sensors of different types, and usually multiple deformable mirrors (DMs). Here, we report on our experience integrating cameras and DMs with the real-time control systems of two wide-field AO systems. These are CANARY, which has been operating on-sky since 2010, and DRAGON, which is a laboratory AO real-time demonstrator instrument. We detail the issues and difficulties that arose, along with the solutions we developed. We also provide recommendations for consideration when developing future wide-field AO systems.

CROWN-C: A High-Assurance Service-Oriented Grid Middleware System

Service-orientation is a highly useful means of developing flexible, agile, and dependable software systems, and is a paradigm that has been increasingly adopted into grid computing middleware. However, service-orientation brings with it new challenges in the fields of dependability and security that need to be addressed by the high assurance systems community in order to provide sufficient support to enable service- based grid applications to offer non-trivial quality of service guarantees. This paper discusses some of the new dependability and security challenges introduced by service-orientation, and for the first time introduces CROWN-C - a grid middleware system that features specific enhancements designed to support the development and assessment of highly secure, dependable, service-oriented grid systems and applications. The architecture of the new middleware is discussed, and the architecture and functionality of each dependability and security enhancement is described, alongside the results of experimental evaluations of each enhancement. Future work is then discussed.

Dependability Assessment of Grid Middleware

Dependability is a key factor in any software system due to the potential costs in both time and money a failure may cause. Given the complexity of grid applications that rely on dependable grid middleware, tools for the assessment of grid middleware are highly desirable. Our past research, based around our fault injection technology (FIT) framework and its implementation, WS-FIT, has demonstrated that network level fault injection can be a valuable tool in assessing the dependability of traditional Web services. Here we apply our FIT framework to globus grid middleware using grid-FIT, our new implementation of the FIT framework, to obtain middleware dependability assessment data. We conclude by demonstrating that grid-FIT can be applied to globus grid systems to assess dependability as part of a fault removal mechanism and thus allow middleware dependability to be increased.

An ontology-based approach for determining the dependability of service-oriented architectures

This paper introduces our novel ontologies for the generation of fault injection test cases and failure detection. Our first ontology is an extension of a standard fault model that is constructed through decomposition to create a framework that facilitates automatic test generation. The second ontology is based on a set of failure modes and again decomposed to create a framework to aid in the automatic detection of system failures. We demonstrate the WS-FIT method and fault injection tools with the use of a simulated real-world system.