4,144 research outputs found
Ground states and thermal states of the random field Ising model
The random field Ising model is studied numerically at both zero and positive
temperature. Ground states are mapped out in a region of random and external
field strength. Thermal states and thermodynamic properties are obtained for
all temperatures using the the Wang-Landau algorithm. The specific heat and
susceptibility typically display sharp peaks in the critical region for large
systems and strong disorder. These sharp peaks result from large domains
flipping. For a given realization of disorder, ground states and thermal states
near the critical line are found to be strongly correlated--a concrete
manifestation of the zero temperature fixed point scenario.Comment: 5 pages, 5 figures; new material added in this versio
Numerical study of the random field Ising model at zero and positive temperature
In this paper the three dimensional random field Ising model is studied at
both zero temperature and positive temperature. Critical exponents are
extracted at zero temperature by finite size scaling analysis of large
discontinuities in the bond energy. The heat capacity exponent is
found to be near zero. The ground states are determined for a range of external
field and disorder strength near the zero temperature critical point and the
scaling of ground state tilings of the field-disorder plane is discussed. At
positive temperature the specific heat and the susceptibility are obtained
using the Wang-Landau algorithm. It is found that sharp peaks are present in
these physical quantities for some realizations of systems sized and
larger. These sharp peaks result from flipping large domains and correspond to
large discontinuities in ground state bond energies. Finally, zero temperature
and positive temperature spin configurations near the critical line are found
to be highly correlated suggesting a strong version of the zero temperature
fixed point hypothesis.Comment: 11 pages, 14 figure
Complex networks in climate dynamics - Comparing linear and nonlinear network construction methods
Complex network theory provides a powerful framework to statistically
investigate the topology of local and non-local statistical interrelationships,
i.e. teleconnections, in the climate system. Climate networks constructed from
the same global climatological data set using the linear Pearson correlation
coefficient or the nonlinear mutual information as a measure of dynamical
similarity between regions, are compared systematically on local, mesoscopic
and global topological scales. A high degree of similarity is observed on the
local and mesoscopic topological scales for surface air temperature fields
taken from AOGCM and reanalysis data sets. We find larger differences on the
global scale, particularly in the betweenness centrality field. The global
scale view on climate networks obtained using mutual information offers
promising new perspectives for detecting network structures based on nonlinear
physical processes in the climate system.Comment: 24 pages, 10 figure
Book review: uneasy street: the anxieties of affluence by Rachel Sherman
In Uneasy Street: The Anxieties of Affluence, Rachel Sherman undertakes 50 in-depth interviews with rich New Yorkers to consider how they navigate their anxieties and the negative connotations surrounding extreme wealth. The frank accounts offered in the book provide a complex picture of elite consumption and the attempt to reconcile affluence and moral legitimacy, finds Jonathan Yong Tienxhi
Cavity ring-up spectroscopy for dissipative and dispersive sensing in a whispering gallery mode resonator
In whispering gallery mode resonator sensing applications, the conventional
way to detect a change in the parameter to be measured is by observing the
steady state transmission spectrum through the coupling waveguide.
Alternatively, cavity ring-up spectroscopy (CRUS) sensing can be achieved
transiently. In this work, we investigate CRUS using coupled mode equations and
find analytical solutions with a large spectral broadening approximation of the
input pulse. The relationships between the frequency detuning, coupling gap and
ring-up peak height are determined and experimentally verified using an
ultrahigh \textit{Q}-factor silica microsphere. This work shows that
distinctive dispersive and dissipative transient sensing can be realised by
simply measuring the peak height of the CRUS signal, which might improve the
data collection rate
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