5,069 research outputs found
Dynamics and Steady States in excitable mobile agent systems
We study the spreading of excitations in 2D systems of mobile agents where
the excitation is transmitted when a quiescent agent keeps contact with an
excited one during a non-vanishing time. We show that the steady states
strongly depend on the spatial agent dynamics. Moreover, the coupling between
exposition time () and agent-agent contact rate (CR) becomes crucial to
understand the excitation dynamics, which exhibits three regimes with CR: no
excitation for low CR, an excited regime in which the number of quiescent
agents (S) is inversely proportional to CR, and for high CR, a novel third
regime, model dependent, here S scales with an exponent , with
being the scaling exponent of with CR
Phase separation and electron pairing in repulsive Hubbard clusters
Exact thermal studies of small (4-site, 5-site and 8-site)
Hubbard clusters with local electron repulsion yield intriguing insight into
phase separation, charge-spin separation, pseudogaps, condensation, in
particular, pairing fluctuations away from half filling (near optimal doping).
These exact calculations, carried out in canonical (i.e. for fixed electron
number N) and grand canonical (i.e. fixed chemical potential ) ensembles,
monitoring variations in temperature T and magnetic field h, show rich phase
diagrams in a T- space consisting of pairing fluctuations and signatures
of condensation. These electron pairing instabilities are seen when the onsite
Coulomb interaction U is smaller than a critical value U(T) and they point
to a possible electron pairing mechanism. The specific heat, magnetization,
charge pairing and spin pairing provide strong support for the existence of
competing (paired and unpaired) phases near optimal doping in these clusters as
observed in recent experiments in doped LaSrCuO high T
superconductors.Comment: 5 pages, 5 figure
Local electronic nematicity in the one-band Hubbard model
Nematicity is a well known property of liquid crystals and has been recently
discussed in the context of strongly interacting electrons. An electronic
nematic phase has been seen by many experiments in certain strongly correlated
materials, in particular, in the pseudogap phase generic to many hole-doped
cuprate superconductors. Recent measurements in high superconductors has
shown even if the lattice is perfectly rotationally symmetric, the ground state
can still have strongly nematic local properties. Our study of the
two-dimensional Hubbard model provides strong support of the recent
experimental results on local rotational symmetry breaking. The
variational cluster approach is used here to show the possibility of an
electronic nematic state and the proximity of the underlying symmetry-breaking
ground state within the Hubbard model. We identify this nematic phase in the
overdoped region and show that the local nematicity decreases with increasing
electron filling. Our results also indicate that strong Coulomb interaction may
drive the nematic phase into a phase similar to the stripe structure. The
calculated spin (magnetic) correlation function in momentum space shows the
effects resulting from real-space nematicity
Thermodynamics of Born-Infeld-anti-de Sitter black holes in the grand canonical ensemble
The main objective of this paper is to study thermodynamics and stability of
static electrically charged Born-Infeld black holes in AdS space in D=4. The
Euclidean action for the grand canonical ensemble is computed with the
appropriate boundary terms. The thermodynamical quantities such as the Gibbs
free energy, entropy and specific heat of the black holes are derived from it.
The global stability of black holes are studied in detail by studying the free
energy for various potentials. For small values of the potential, we find that
there is a Hawking-Page phase transition between a BIAdS black hole and the
thermal-AdS space. For large potentials, the black hole phase is dominant and
are preferred over the thermal-AdS space. Local stability is studied by
computing the specific heat for constant potentials. The non-extreme black
holes have two branches: small black holes are unstable and the large black
holes are stable. The extreme black holes are shown to be stable both globally
as well as locally. In addition to the thermodynamics, we also show that the
phase structure relating the mass and the charge of the black holes is
similar to the liquid-gas-solid phase diagram.Comment: Accepted to be published in Physical Review D. Minor change
Observation of a Griffiths-like phase in the paramagnetic regime of ErCo_2
A systematic x-ray magnetic circular dichroism study of the paramagnetic
phase of ErCo2 has recently allowed to identify the inversion of the net
magnetization of the Co net moment with respect to the applied field well above
the ferrimagnetic ordering temperature, Tc. The study of small angle neutron
scattering measurements has also shown the presence of short range order
correlations in the same temperature region. This phenomenon, which we have
denoted parimagnetism, may be related with the onset of a Griffiths-like phase
in paramagnetic ErCo2. We have measured ac susceptibility on ErCo2 as a
function of temperature, applied field, and excitation frequency. Several
characteristics shared by systems showing a Griffiths phase are present in
ErCo2, namely the formation of ferromagnetic clusters in the disordered phase,
the loss of analyticity of the magnetic susceptibility and its extreme
sensitivity to an applied magnetic field. The paramagnetic susceptibility
allows to establish that the magnetic clusters are only formed by Co moments as
well as the intrinsic nature of those Co moments
Tracing magnetism and pairing in FeTe-based systems
In order to examine the interplay between magnetism and superconductivity, we
monitor the non- superconducting chalcogenide FeTe and follow its transitions
under insertion of oxygen, doping with Se and vacancies of Fe using
spin-polarized band structure methods (LSDA with GGA) starting from the
collinear and bicollinear magnetic arrangements. We use a supercell of Fe8Te8
as our starting point so that it can capture local changes in magnetic moments.
The calculated values of magnetic moments agree well with available
experimental data while oxygen insertions lead to significant changes in the
bicollinear or collinear magnetic moments. The total energies of these systems
indicate that the collinear-derived structure is the more favorable one prior
to a possible superconducting transition. Using a 8-site Betts-cluster-based
lattice and the Hubbard model, we show why this structure favors electron or
hole pairing and provides clues to a common understanding of charge and spin
pairing in the cuprates, pnictides and chalcogenides
Post-crisis recovery management of tourism: Lesson Learnt from the Easter Sunday attack in Sri Lanka
International tourism has evolved into one of the largest global economic sectors, contributing significantly to many national and local economies. However, the crises have caused much loss and damage over the last few decades, burdening the tourism industry. On April 21, 2019, the day of Easter Sunday, Sri Lanka experienced a series of unexpected attacks. It caused many problems and challenges to the tourism industry. This study attempts to understand respondents who are involved in the tourism industry's lived experiences of the Sunday easter attack and their involvement in recovery. The qualitative research method, particularly the phenomenological approach, was adopted to collect and analyse data through the lens of the stakeholder theory. Senior managers representing the different tourism industry sectors were purposively approached and interviewed. Data were analysed using thematic analysis. Findings revealed that the easter Sunday attack negatively influenced the number of tourist arrivals and experiences. However, a well-designed crisis management plan under the control of the official authority can minimise the risk and reduce the negative impact of the incident. Therefore, this study presents an innovative integrated model that could be used as a crisis management plan to restore the tourism industry.
Keywords: Disaster, Easter Sunday attack, Recovery process, Tourism, Phenomenology, Stakeholder theory  
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