1,737 research outputs found
Statistical mechanics of the international trade network
Analyzing real data on international trade covering the time interval
1950-2000, we show that in each year over the analyzed period the network is a
typical representative of the ensemble of maximally random weighted networks,
whose directed connections (bilateral trade volumes) are only characterized by
the product of the trading countries' GDPs. It means that time evolution of
this network may be considered as a continuous sequence of equilibrium states,
i.e. quasi-static process. This, in turn, allows one to apply the linear
response theory to make (and also verify) simple predictions about the network.
In particular, we show that bilateral trade fulfills fluctuation-response
theorem, which states that the average relative change in import (export)
between two countries is a sum of relative changes in their GDPs. Yearly
changes in trade volumes prove that the theorem is valid.Comment: 6 pages, 2 figure
Supremacy distribution in evolving networks
We study a supremacy distribution in evolving Barabasi-Albert networks. The
supremacy of a node is defined as a total number of all nodes that
are younger than and can be connected to it by a directed path. For a
network with a characteristic parameter the supremacy of an
individual node increases with the network age as in an
appropriate scaling region. It follows that there is a relation between a node degree and its supremacy and the supremacy
distribution scales as . Analytic calculations basing on
a continuum theory of supremacy evolution and on a corresponding rate equation
have been confirmed by numerical simulations.Comment: 4 pages, 4 figure
Effect of relativistic acceleration on localized two-mode Gaussian quantum states
We study how an arbitrary Gaussian state of two localized wave packets,
prepared in an inertial frame of reference, is described by a pair of uniformly
accelerated observers. We explicitly compute the resulting state for
arbitrarily chosen proper accelerations of the observers and independently
tuned distance between them. To do so, we introduce a generalized Rindler frame
of reference and analytically derive the corresponding state transformation as
a Gaussian channel. Our approach provides several new insights into the
phenomenon of vacuum entanglement such as the highly non-trivial effect of
spatial separation between the observers including sudden death of
entanglement. We also calculate the fidelity of the two-mode channel for
non-vacuum Gaussian states and obtain bounds on classical and quantum
capacities of a single-mode channel. Our framework can be directly applied to
any continuous variable quantum information protocol in which the effects of
acceleration or gravity cannot be neglected.Comment: 21 pages, 13 figures. A few typos correcte
Ferromagnetic fluid as a model of social impact
The paper proposes a new model of spin dynamics which can be treated as a
model of sociological coupling between individuals. Our approach takes into
account two different human features: gregariousness and individuality. We will
show how they affect a psychological distance between individuals and how the
distance changes the opinion formation in a social group. Apart from its
sociological aplications the model displays the variety of other interesting
phenomena like self-organizing ferromagnetic state or a second order phase
transition and can be studied from different points of view, e.g. as a model of
ferromagnetic fluid, complex evolving network or multiplicative random process.Comment: 8 pages, 5 figure
Limits to sustained energy intake. XXIII. Does heat dissipation capacity limit the energy budget of lactating bank voles?
Acknowledgements We are grateful to our technicians and several students for their help during this study and for animal care. We thank Catherine Hambly and Peter Thompson for technical assistance for the isotope analysis for the DLW measurements. We thank Ulf Bauchinger for stimulating discussion and his comments, and two anonymous referees for comments on the manuscript. Funding This project was supported by grants from the Polish Ministry of Science and Higher Education [0595/B/P01/2011/40 to E.T.S. and 8167/B/P01/2011/40 to P.K.], and Jagiellonian University [DS/WBINOZ/INOS/757 to P.K.].Peer reviewedPublisher PD
Modelling optical micro-machines
A strongly focused laser beam can be used to trap, manipulate and exert
torque on a microparticle. The torque is the result of transfer of angular
momentum by scattering of the laser beam. The laser could be used to drive a
rotor, impeller, cog wheel or some other microdevice of a few microns in size,
perhaps fabricated from a birefringent material. We review our methods of
computationally simulating the torque and force imparted by a laser beam. We
introduce a method of hybridizing the T-matrix with the Finite Difference
Frequency Domain (FDFD) method to allow the modelling of materials that are
anisotropic and inhomogeneous, and structures that have complex shapes. The
high degree of symmetry of a microrotor, such as discrete or continuous
rotational symmetry, can be exploited to reduce computational time and memory
requirements by orders of magnitude. This is achieved by performing
calculations for only a given segment or plane that is repeated across the
whole structure. This can be demonstrated by modelling the optical trapping and
rotation of a cube.Comment: 4 pages, 3 figure
Tracking sand-fairways through a deformed turbidite system : the Numidian (Miocene) of Central Sicily, Italy
The research presented here is funded by BG Group in partnership with CNPq-Brazil (National Council for Scientific and Technological Development). Rosanna Maniscalco acknowledges a FIR 2014 grant awarded from the University of Catania. We thank Christian Haug Eide, David Hodgson and Enrico Tavarnelli for constructive and thorough reviews on an earlier draft that have greatly improved this contribution.Peer reviewedPublisher PD
Dissipation enhanced vibrational sensing in an olfactory molecular switch
Motivated by a proposed olfactory mechanism based on a
vibrationally-activated molecular switch, we study electron transport within a
donor-acceptor pair that is coupled to a vibrational mode and embedded in a
surrounding environment. We derive a polaron master equation with which we
study the dynamics of both the electronic and vibrational degrees of freedom
beyond previously employed semiclassical (Marcus-Jortner) rate analyses. We
show: (i) that in the absence of explicit dissipation of the vibrational mode,
the semiclassical approach is generally unable to capture the dynamics
predicted by our master equation due to both its assumption of one-way
(exponential) electron transfer from donor to acceptor and its neglect of the
spectral details of the environment; (ii) that by additionally allowing strong
dissipation to act on the odorant vibrational mode we can recover exponential
electron transfer, though typically at a rate that differs from that given by
the Marcus-Jortner expression; (iii) that the ability of the molecular switch
to discriminate between the presence and absence of the odorant, and its
sensitivity to the odorant vibrational frequency, are enhanced significantly in
this strong dissipation regime, when compared to the case without mode
dissipation; and (iv) that details of the environment absent from previous
Marcus-Jortner analyses can also dramatically alter the sensitivity of the
molecular switch, in particular allowing its frequency resolution to be
improved. Our results thus demonstrate the constructive role dissipation can
play in facilitating sensitive and selective operation in molecular switch
devices, as well as the inadequacy of semiclassical rate equations in analysing
such behaviour over a wide range of parameters.Comment: 12 pages, 6 figures, close to published version, comments welcom
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