1,848 research outputs found
Possible ion-acoustic soliton formation in the ionospheric perturbations observed on DEMETER before the 2007 Pu'er earthquake
The data of ionospheric perturbations observed on DEMETER before the 2007 Pu'er earthquake are analyzed. The three-component plasma (ions, electrons and heavy ions) is studied in the fluid concept. The linear dispersion relation for ion-acoustic wave is found in the presence of heavy ions. The nonlinear dynamics is studied for arbitrary amplitude of the wave. The Sagdeev potential is calculated, which shows that solitary structure exists for Mach number within a range defined by the presence of heavy ions. The developed ion-acoustic solitons may be used as precursor for earthquake prediction
Gravitational Waves from Rotating Proto-Neutron Stars
We study the effects of rotation on the quasi normal modes (QNMs) of a newly
born proto neutron star (PNS) at different evolutionary stages, until it
becomes a cold neutron star (NS). We use the
Cowling approximation, neglecting spacetime perturbations, and consider
different models of evolving PNS. The frequencies of the modes of a PNS are
considerably lower than those of a cold NS, and are further lowered by
rotation; consequently, if QNMs were excited in a sufficiently energetic
process, they would radiate waves that could be more easily detectable by
resonant-mass and interferometric detectors than those emitted by a cold NS. We
find that for high rotation rates, some of the g-modes become unstable via the
CFS instability; however, this instability is likely to be suppressed by
competing mechanisms before emitting a significant amount of gravitational
waves.Comment: 5 pages, proceedings of the 5th Edoardo Amaldi Conference On
Gravitational Wave
Backbone of complex networks of corporations: The flow of control
We present a methodology to extract the backbone of complex networks based on
the weight and direction of links, as well as on nontopological properties of
nodes. We show how the methodology can be applied in general to networks in
which mass or energy is flowing along the links. In particular, the procedure
enables us to address important questions in economics, namely, how control and
wealth are structured and concentrated across national markets. We report on
the first cross-country investigation of ownership networks, focusing on the
stock markets of 48 countries around the world. On the one hand, our analysis
confirms results expected on the basis of the literature on corporate control,
namely, that in Anglo-Saxon countries control tends to be dispersed among
numerous shareholders. On the other hand, it also reveals that in the same
countries, control is found to be highly concentrated at the global level,
namely, lying in the hands of very few important shareholders. Interestingly,
the exact opposite is observed for European countries. These results have
previously not been reported as they are not observable without the kind of
network analysis developed here.Comment: 24 pages, 12 figures, 2nd version (text made more concise and
readable, results unchanged
Credit Default Swaps Drawup Networks: Too Tied To Be Stable?
We analyse time series of CDS spreads for a set of major US and European
institutions on a pe- riod overlapping the recent financial crisis. We extend
the existing methodology of {\epsilon}-drawdowns to the one of joint
{\epsilon}-drawups, in order to estimate the conditional probabilities of
abrupt co-movements among spreads. We correct for randomness and for finite
size effects and we find significant prob- ability of joint drawups for certain
pairs of CDS. We also find significant probability of trend rein- forcement,
i.e. drawups in a given CDS followed by drawups in the same CDS. Finally, we
take the matrix of probability of joint drawups as an estimate of the network
of financial dependencies among institutions. We then carry out a network
analysis that provides insights into the role of systemically important
financial institutions.Comment: 15 pages, 5 figures, Supplementary informatio
Organoindium precursor purification by new sorbents based on titanium and zirconium phosphates
High purity requirements for organometallic precursors have recently become critical in the field of III–V semiconductor films obtained by chemical vapour deposition techniques. Traditional purification routes employing physical methods need to be replaced by ones which are more rapid and effective. Such a route is described in this paper. This involves the elimination of any traces of impurity by applying several combinations of sorbents. In this way, complete elimination of lithium impurities introduced during precursor synthesis has been achieved by the use of titanium or zirconium phosphate sorbents (usually used as acidic ion exchangers in aqueous media). The method also preserves the stability of the organoindium precursor which is normally extremely sensitive to moisture. A possible explanation for these observations is given
Fracture–dislocations of the forearm joint: a systematic review of the literature and a comprehensive locker-based classification system
Networks of companies and branches in Poland
In this study we consider relations between companies in Poland taking into
account common branches they belong to. It is clear that companies belonging to
the same branch compete for similar customers, so the market induces
correlations between them. On the other hand two branches can be related by
companies acting in both of them. To remove weak, accidental links we shall use
a concept of threshold filtering for weighted networks where a link weight
corresponds to a number of existing connections (common companies or branches)
between a pair of nodes.Comment: 13 pages, 10 figures and 4 table
Topological enslavement in evolutionary games on correlated multiplex networks
Governments and enterprises strongly rely on incentives to generate favorable
outcomes from social and strategic interactions between individuals. The
incentives are usually modeled by payoffs in evolutionary games, such as the
prisoner's dilemma or the harmony game, with imitation dynamics. Adjusting the
incentives by changing the payoff parameters can favor cooperation, as found in
the harmony game, over defection, which prevails in the prisoner's dilemma.
Here, we show that this is not always the case if individuals engage in
strategic interactions in multiple domains. In particular, we investigate
evolutionary games on multiplex networks where individuals obtain an aggregate
payoff. We explicitly control the strength of degree correlations between nodes
in the different layers of the multiplex. We find that if the multiplex is
composed of many layers and degree correlations are strong, the topology of the
system enslaves the dynamics and the final outcome, cooperation or defection,
becomes independent of the payoff parameters. The fate of the system is then
determined by the initial conditions
Web search queries can predict stock market volumes
We live in a computerized and networked society where many of our actions leave a digital trace and affect other people's actions. This has lead to the emergence of a new data-driven research field: mathematical methods of computer science, statistical physics and sociometry provide insights on a wide range of disciplines ranging from social science to human mobility. A recent important discovery is that search engine traffic (i.e., the number of requests submitted by users to search engines on the www) can be used to track and, in some cases, to anticipate the dynamics of social phenomena. Successful examples include unemployment levels, car and home sales, and epidemics spreading. Few recent works applied this approach to stock prices and market sentiment. However, it remains unclear if trends in financial markets can be anticipated by the collective wisdom of on-line users on the web. Here we show that daily trading volumes of stocks traded in NASDAQ-100 are correlated with daily volumes of queries related to the same stocks. In particular, query volumes anticipate in many cases peaks of trading by one day or more. Our analysis is carried out on a unique dataset of queries, submitted to an important web search engine, which enable us to investigate also the user behavior. We show that the query volume dynamics emerges from the collective but seemingly uncoordinated activity of many users. These findings contribute to the debate on the identification of early warnings of financial systemic risk, based on the activity of users of the www. © 2012 Bordino et al
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