6,037 research outputs found
Sequential Decision Making with Untrustworthy Service Providers
In this paper, we deal with the sequential decision making problem of agents operating in computational economies, where there is uncertainty regarding the trustworthiness of service providers populating the environment. Specifically, we propose a generic Bayesian trust model, and formulate the optimal Bayesian solution to the exploration-exploitation problem facing the agents when repeatedly interacting with others in such environments. We then present a computationally tractable Bayesian reinforcement learning algorithm to approximate that solution by taking into account the expected value of perfect information of an agent's actions. Our algorithm is shown to dramatically outperform all previous finalists of the international Agent Reputation and Trust (ART) competition, including the winner from both years the competition has been run
Semi-transparent brane-worlds
We study the evolution of a closed Friedmann brane perturbed by the Hawking
radiation escaping a bulk black hole. The semi-transparent brane absorbes some
of the infalling radiation, the rest being transmitted across the brane to the
other bulk region. We characterize the cosmological evolution in terms of the
transmission rate . For small values of a critical-like
behaviour could be observed, when the acceleration due to radiation pressure
and the deceleration induced by the increasing self-gravity of the brane
roughly compensate each other, and cosmological evolution is approximately the
same as without radiation. Lighter (heavier) branes than those with the
critical energy density will recollapse slower (faster). This feature is
obstructed at high values of , where the overall effect of the
radiation is to speed-up the recollapse. We determine the maximal value of the
transmission rate for which the critical-like behaviour is observed. We also
study the effect of transmission on the evolution of different source terms of
the Friedmann equation. We conclude that among all semi-transparent branes the
slowest recollapse occurs for light branes with total absorption.Comment: 15 pages, 8 figure
On the response of a particle detector in Anti-de Sitter spacetime
We consider the vacuum response of a particle detector in Anti-de Sitter
spacetime, and in particular analyze how spacetime features such as curvature
and dimensionality affect the response spectrum of an accelerated detector. We
calculate useful limits on Wightman functions, analyze the dynamics of the
detector in terms of vacuum fluctuations and radiation reactions, and discuss
the thermalization process for the detector. We also present a generalization
of the GEMS approach and obtain the Gibbons-Hawking temperature of de Sitter
spacetime as an embedded Unruh temperature in a curved Anti-de Sitter
spacetime.Comment: 13 pages, no figures, accepted for publication in Class. Quantum Gra
Combined ablation and radiation therapy of spinal metastases: A novel multimodality treatment approach
What kind of Brexit do voters want? Lessons from the Citizens’ Assembly on Brexit
The Citizens’ Assembly on Brexit was a major exercise in deliberative public engagement conducted in autumn 2017. It brought together fifty randomly selected members of the public for two carefully structured weekends of listening, learning, reflecting and discussing. Assembly Members considered what post-Brexit arrangements the UK should pursue, focusing on trade and migration. On trade, most Members wanted the UK to pursue a bespoke arrangement with the EU and rejected the option of leaving the EU with no deal. On migration, most wanted the UK to maintain free movement of labour while using already available policy levers to reduce immigration numbers. These findings provide unique insight into informed public opinion on vital, pressing policy questions. The Assembly also illustrates the valuable role that such deliberative exercises could play in UK democracy. We suggest they could be particular helpful for unlocking progress on issues, such as the future of social care, that are often felt to be ‘too difficult’ to handle
The position profiles of order cancellations in an emerging stock market
Order submission and cancellation are two constituent actions of stock
trading behaviors in order-driven markets. Order submission dynamics has been
extensively studied for different markets, while order cancellation dynamics is
less understood. There are two positions associated with a cancellation, that
is, the price level in the limit-order book (LOB) and the position in the queue
at each price level. We study the profiles of these two order cancellation
positions through rebuilding the limit-order book using the order flow data of
23 liquid stocks traded on the Shenzhen Stock Exchange in the year 2003. We
find that the profiles of relative price levels where cancellations occur obey
a log-normal distribution. After normalizing the relative price level by
removing the factor of order numbers stored at the price level, we find that
the profiles exhibit a power-law scaling behavior on the right tails for both
buy and sell orders. When focusing on the order cancellation positions in the
queue at each price level, we find that the profiles increase rapidly in the
front of the queue, and then fluctuate around a constant value till the end of
the queue. These profiles are similar for different stocks. In addition, the
profiles of cancellation positions can be fitted by an exponent function for
both buy and sell orders. These two kinds of cancellation profiles seem
universal for different stocks investigated and exhibit minor asymmetry between
buy and sell orders. Our empirical findings shed new light on the order
cancellation dynamics and pose constraints on the construction of order-driven
stock market models.Comment: 17 pages, 6 figures and 6 table
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