22,041 research outputs found
The emergence of classical behavior in magnetic adatoms
A wide class of nanomagnets shows striking quantum behavior, known as quantum
spin tunneling (QST): instead of two degenerate ground states with opposite
magnetizations, a bonding-antibonding pair forms, resulting in a splitting of
the ground state doublet with wave functions linear combination of two
classically opposite magnetic states, leading to the quenching of their
magnetic moment. Here we study how QST is destroyed and classical behavior
emerges in the case of magnetic adatoms, as the strength of their coupling,
either to the substrate or to each other, is increased. Both spin-substrate and
spin-spin coupling renormalize the QST splitting to zero allowing the
environmental decoherence to eliminate superpositions between classical states,
leading to the emergence of spontaneous magnetization.Comment: 5 pages, 4 figure
DMRG study of the Bond Alternating \textbf{S}=1/2 Heisenberg ladder with Ferro-Antiferromagnetic couplings
We obtain the phase diagram in the parameter space and an
accurate estimate of the critical line separating the different phases. We show
several measuments of the magnetization, dimerization, nearest neighbours
correlation, and density of energy in the different zones of the phase diagram,
as well as a measurement of the string order parameter proposed as the non
vanishing phase order parameter characterizing Haldane phases. All these
results will be compared in the limit with the behaviour of the
Bond Alternated Heisenberg Chain (BAHC). The analysis of our
data supports the existence of a dimer phase separated by a critical line from
a Haldane one, which has exactly the same nature as the Haldane phase in the
BAHC.Comment: Version 4. 8 pages, 15 figures (12 figures in document
Determination of the chemical potential using energy-biased sampling
An energy-biased method to evaluate ensemble averages requiring test-particle
insertion is presented. The method is based on biasing the sampling within the
subdomains of the test-particle configurational space with energies smaller
than a given value freely assigned. These energy-wells are located via unbiased
random insertion over the whole configurational space and are sampled using the
so called Hit&Run algorithm, which uniformly samples compact regions of any
shape immersed in a space of arbitrary dimensions. Because the bias is defined
in terms of the energy landscape it can be exactly corrected to obtain the
unbiased distribution. The test-particle energy distribution is then combined
with the Bennett relation for the evaluation of the chemical potential. We
apply this protocol to a system with relatively small probability of low-energy
test-particle insertion, liquid argon at high density and low temperature, and
show that the energy-biased Bennett method is around five times more efficient
than the standard Bennett method. A similar performance gain is observed in the
reconstruction of the energy distribution.Comment: 10 pages, 4 figure
Hub operations delay recovery based on cost optimisation - Dynamic cost indexing and waiting for passengers strategies
In this paper, two strategies for airlines’ operations at a hub are combined and analysed: dynamic cost indexing, to recover delay, and waiting for connecting passengers at the hub. Agent Based Modelling techniques have been used to model the airlines’ operations considering detailed passenger’s itineraries, an extended arrival manager operation with slot negotiation, and delay and uncertainty at different phases of the flights. Results show that, when optimising the total cost, there is a trade-off between connecting and non-connecting passengers with respect to the gate to gate trip time. Waiting for passengers arises as an interesting technique when minimising airline operating costs
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