On avoiding Ostrogradski instabilities within Asymptotic Safety

We study the renormalization group flow of gravity coupled to scalar matter using functional renormalization group techniques. The novel feature is the inclusion of higher-derivative terms in the scalar propagator. Such terms give rise to Ostrogradski ghosts which signal an instability of the system and are therefore dangerous for the consistency of the theory. Since it is expected that such terms are generated dynamically by the renormalization group flow they provide a potential threat when constructing a theory of quantum gravity based on Asymptotic Safety. Our work then establishes the following picture: upon incorporating higher-derivative terms in the scalar propagator the flow of the gravity-matter system possesses a fixed point structure suitable for Asymptotic Safety. This structure includes an interacting renormalization group fixed point where the Ostrogradski ghosts acquire an infinite mass and decouple from the system. Tracing the flow towards the infrared it is found that there is a subset of complete renormalization group trajectories which lead to stable renormalized propagators. This subset is in one-to-one correspondence to the complete renormalization group trajectories obtained in computations which do not track of the higher-derivative terms. Thus our asymptotically safe gravity-matter systems are not haunted by Ostrogradski ghosts.Comment: 35 pages, 10 figure

Crowdsourcing Swarm Manipulation Experiments: A Massive Online User Study with Large Swarms of Simple Robots

Micro- and nanorobotics have the potential to revolutionize many applications including targeted material delivery, assembly, and surgery. The same properties that promise breakthrough solutions---small size and large populations---present unique challenges to generating controlled motion. We want to use large swarms of robots to perform manipulation tasks; unfortunately, human-swarm interaction studies as conducted today are limited in sample size, are difficult to reproduce, and are prone to hardware failures. We present an alternative. This paper examines the perils, pitfalls, and possibilities we discovered by launching SwarmControl.net, an online game where players steer swarms of up to 500 robots to complete manipulation challenges. We record statistics from thousands of players, and use the game to explore aspects of large-population robot control. We present the game framework as a new, open-source tool for large-scale user experiments. Our results have potential applications in human control of micro- and nanorobots, supply insight for automatic controllers, and provide a template for large online robotic research experiments.Comment: 8 pages, 13 figures, to appear at 2014 IEEE International Conference on Robotics and Automation (ICRA 2014

Reflection positivity in higher derivative scalar theories

Reflection positivity constitutes an integral prerequisite in the Osterwalder-Schrader reconstruction theorem which relates quantum field theories defined on Euclidean space to their Lorentzian signature counterparts. In this work we rigorously prove the violation of reflection positivity in a large class of free scalar fields with a rational propagator. This covers in particular higher-derivative theories where the propagator admits a partial fraction decomposition as well as degenerate cases including e.g. p^4 -type propagators.Comment: 9 pages, 1 figur

Formation Flying for Satellites and UAVs

A formation monitoring and control system was developed utilizing mesh networking and decentralized control. Highlights of this system include low latency, seamless addition and removal of vehicles, network relay functionality, and the ability to run on a variety of hardware

Volatility in International Capital Movements

Conventional wisdom is that some capital flows are inherently more volatile than others. However, our investigation of the statistical properties of these flows shows that no regular relationships exist to suggest that the particular composition of capital flows can help to explain the overall stability of the external accounts. Instead, capital seems to come and go in different forms with few reliable patterns. We show that while industrialised economies have experienced a trend rise in the volatility of individual components in the capital account, this variability is largely offsetting. Such offsetting relationships appear less prevalent in emerging economies.capital flows; volatility; financial globalisation

Profitability of Reserve Bank Foreign Exchange Operations: Twenty Years After the Float

Since the float of the Australian dollar in December 1983, the Reserve Bank of Australia (RBA) has retained the discretion to intervene in the foreign exchange markets in order to avoid what it perceives to be large overshooting in the currency. In this paper we invoke the ‘profit test’ first advocated by Friedman to assess whether the RBA’s foreign exchange operations have had a stabilising influence on the exchange rate. We do this over the entire post-float period, as well as for each of the three distinct cycles in the exchange rate during that period. The premise underlying the profit test is that if the central bank has made a profit from intervention in its currency, it must have ‘bought low and sold high’, which would work towards stabilising the exchange rate. Since the float, the RBA has made a profit of A$5.2 billion on its intervention operations, with profits made in each of the three cycles. The paper concludes that the profitability of intervention suggests that the RBA’s operations have had a stabilising influence on the exchange rate.intervention; profit test; foreign exchange rate; overshooting

Statistical profile of young carers

In 1995 the first ever quantitative survey of young carers was undertaken. The survey included data about 641 young carers, supported by 36 designated projects across Britain. In 1997 the survey was replicated. By this time there were more support projects for young carers and data were collected about 2303 young carers from 69 projects. These two surveys enabled researchers for the first time to statistically analyse data such as age, ethnicity, caring tasks, cared for person etc. Prior to this the ‘invisibility’ of young carers meant that previous research had been smallscale and qualitative in nature

Sheffield Young Carers Project: an evaluation - interim report April 1997 September 1998

Sheffield Young Carers Project (SYCP) was established in November 1996 when a co-ordinator was appointed for a three year period. This followed a successful joint finance bid by a multi-agency steering group which had been meeting for approximately a year. Joint finance funding was awarded for a three year period, and additional funding from the National Lotteries Charities Board (NLCB) has enabled the Project to employ additional staff. Currently the Project has one full-time co-ordinator, who is employed by and managed by the Education Department of the local authority. Two project workers and an administrator were employed in September 1997 for a three year period, funded by the NLCB grant. One of the project workers is employed to work specifically with young carers from black communities. They are employed directly by the Project and line managed by the coordinator. In addition a careers adviser works at the Project two days a week (increased from one day a week from September 1998). A sessional worker has been employed from August 1998 for one year, and a researcher is researching young carers’ issues for two days a week over a period of three months. The Project has a management committee drawn from a range of local statutory and voluntary organisations