279 research outputs found
Optimal redundancy against disjoint vulnerabilities in networks
Redundancy is commonly used to guarantee continued functionality in networked
systems. However, often many nodes are vulnerable to the same failure or
adversary. A "backup" path is not sufficient if both paths depend on nodes
which share a vulnerability.For example, if two nodes of the Internet cannot be
connected without using routers belonging to a given untrusted entity, then all
of their communication-regardless of the specific paths utilized-will be
intercepted by the controlling entity.In this and many other cases, the
vulnerabilities affecting the network are disjoint: each node has exactly one
vulnerability but the same vulnerability can affect many nodes. To discover
optimal redundancy in this scenario, we describe each vulnerability as a color
and develop a "color-avoiding percolation" which uncovers a hidden
color-avoiding connectivity. We present algorithms for color-avoiding
percolation of general networks and an analytic theory for random graphs with
uniformly distributed colors including critical phenomena. We demonstrate our
theory by uncovering the hidden color-avoiding connectivity of the Internet. We
find that less well-connected countries are more likely able to communicate
securely through optimally redundant paths than highly connected countries like
the US. Our results reveal a new layer of hidden structure in complex systems
and can enhance security and robustness through optimal redundancy in a wide
range of systems including biological, economic and communications networks.Comment: 15 page
Regularities and Irregularities in Order Flow Data
We identify and analyze statistical regularities and irregularities in the
recent order flow of different NASDAQ stocks, focusing on the positions where
orders are placed in the orderbook. This includes limit orders being placed
outside of the spread, inside the spread and (effective) market orders. We find
that limit order placement inside the spread is strongly determined by the
dynamics of the spread size. Most orders, however, arrive outside of the
spread. While for some stocks order placement on or next to the quotes is
dominating, deeper price levels are more important for other stocks. As market
orders are usually adjusted to the quote volume, the impact of market orders
depends on the orderbook structure, which we find to be quite diverse among the
analyzed stocks as a result of the way limit order placement takes place.Comment: 10 pages, 9 figure
Spontaneous centralization of control in a network of company ownerships
We introduce a model for the adaptive evolution of a network of company
ownerships. In a recent work it has been shown that the empirical global
network of corporate control is marked by a central, tightly connected "core"
made of a small number of large companies which control a significant part of
the global economy. Here we show how a simple, adaptive "rich get richer"
dynamics can account for this characteristic, which incorporates the increased
buying power of more influential companies, and in turn results in even higher
control. We conclude that this kind of centralized structure can emerge without
it being an explicit goal of these companies, or as a result of a
well-organized strategy.Comment: 5 Pages, 7 figure
Impact and Recovery Process of Mini Flash Crashes: An Empirical Study
In an Ultrafast Extreme Event (or Mini Flash Crash), the price of a traded
stock increases or decreases strongly within milliseconds. We present a
detailed study of Ultrafast Extreme Events in stock market data. In contrast to
popular belief, our analysis suggests that most of the Ultrafast Extreme Events
are not primarily due to High Frequency Trading. In at least 60 percent of the
observed Ultrafast Extreme Events, the main cause for the events are large
market orders. In times of financial crisis, large market orders are more
likely which can be linked to the significant increase of Ultrafast Extreme
Events occurrences. Furthermore, we analyze the 100 trades following each
Ultrafast Extreme Events. While we observe a tendency of the prices to
partially recover, less than 40 percent recover completely. On the other hand
we find 25 percent of the Ultrafast Extreme Events to be almost recovered after
only one trade which differs from the usually found price impact of market
orders
Two Price Regimes in Limit Order Books: Liquidity Cushion and Fragmented Distant Field
The distribution of liquidity within the limit order book is essential for
the impact of market orders on the stock price and the emergence of price
shocks. Hence it is of great interest to improve the understanding of the
time-dependent dynamics of the limit order book. In our analysis we find a
broad distribution of limit order lifetimes. Around the quotes we find a
densely filled regime with mostly short living limit orders, far away from the
quotes we find a sparse filling with mostly long living limit orders. We
determine the characteristics of those two regimes and point out the main
differences. Based on our research we propose a model for simulating the regime
around the quotes
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