1,094 research outputs found
Antiferromagnetism and superfluidity of a dipolar Fermi gas in a 2D optical lattice
In a dipolar Fermi gas, the dipole-dipole interaction between fermions can be
turned into a dipolar Ising interaction between pseduospins in the presence of
an AC electric field. When trapped in a 2D optical lattice, such a dipolar
Fermi gas has a very rich phase diagram at zero temperature, due to the
competition between antiferromagnetism and superfluidity. At half filling, the
antiferromagnetic state is the favored ground state. The superfluid state
appears as the ground state at a smaller filling factor. In between there is a
phase-separated region. The order parameter of the superfluid state can display
different symmetries depending on the filling factor and interaction strength,
including d-wave (), extend s-wave (), or their linear combination
(). The implication for the current experiment is discussed.Comment: 11 pages, 3 figures, references update
Topological Superfluid Phase of a Dipolar Fermi Gas in a 2D Optical Lattice
In a dipolar Fermi gas, the anisotropic interaction between electric dipoles
can be turned into an effectively attractive interaction in the presence of a
rotating electric field. We show that the topological superfluid
phase can be realized in a single-component dipolar Fermi gas trapped in a 2D
square optical lattice with this attractive interaction at low temperatures.
The superfluid state has potential applications for topological
quantum computing. We obtain the phase diagram of this system at zero
temperature. In the weak-coupling limit, the p-wave superfluid phase is stable
for all filling factors. As the interaction strength increases, it is stable
close to filling factors or , and phase separation takes place in
between. When the interaction strength is above a threshold, the system is
phase separated for any . The transition temperature of the
superfluid state is estimated and the implication for
experiments is discussed.Comment: 10 pages, 4 figure
Correlation energy of a homogeneous dipolar Fermi gas
We study the normal state of a 3- homogeneous dipolar Fermi gas beyond the
Hartree-Fock approximation. The correlation energy is found of the same order
as the Fock energy, unusually strong for a Fermi-liquid system. As a result,
the critical density of mechanical collapse is smaller than that estimated in
the Hartree-Fock approximation. With the correlation energy included, a new
energy functional is proposed for the trapped system, and its property is
explored.Comment: 10 pages, 2 figure
Crime Prediction with Historical Crime and Movement Data of Potential Offenders Using a Spatio-Temporal Cokriging Method
Crime prediction using machine learning and data fusion assimilation has become a hot topic. Most of the models rely on historical crime data and related environment variables. The activity of potential offenders affects the crime patterns, but the data with fine resolution have not been applied in the crime prediction. The goal of this study is to test the effect of the activity of potential offenders in the crime prediction by combining this data in the prediction models and assessing the prediction accuracies. This study uses the movement data of past offenders collected in routine police stop-and-question operations to infer the movement of future offenders. The offender movement data compensates historical crime data in a Spatio-Temporal Cokriging (ST-Cokriging) model for crime prediction. The models are implemented for weekly, biweekly, and quad-weekly prediction in the XT police district of ZG city, China. Results with the incorporation of the offender movement data are consistently better than those without it. The improvement is most pronounced for the weekly model, followed by the biweekly model, and the quad-weekly model. In sum, the addition of offender movement data enhances crime prediction, especially for short periods
Assessing the Impact of Nightlight Gradients on Street Robbery and Burglary in Cincinnati of Ohio State, USA
Previous research has recognized the importance of edges to crime. Various scholars have explored how one specific type of edges such as physical edges or social edges affect crime, but rarely investigated the importance of the composite edge effect. To address this gap, this study introduces nightlight data from the Visible Infrared Imaging Radiometer Suite sensor on the Suomi National Polar-orbiting Partnership Satellite (NPP-VIIRS) to measure composite edges. This study defines edges as nightlight gradients—the maximum change of nightlight from a pixel to its neighbors. Using nightlight gradients and other control variables at the tract level, this study applies negative binomial regression models to investigate the effects of edges on the street robbery rate and the burglary rate in Cincinnati. The Akaike Information Criterion (AIC) of models show that nightlight gradients improve the fitness of models of street robbery and burglary. Also, nightlight gradients make a positive impact on the street robbery rate whilst a negative impact on the burglary rate, both of which are statistically significant under the alpha level of 0.05. The different impacts on these two types of crimes may be explained by the nature of crimes and the in-situ characteristics, including nightlight
Bilateral Dependency Optimization: Defending Against Model-inversion Attacks
Through using only a well-trained classifier, model-inversion (MI) attacks
can recover the data used for training the classifier, leading to the privacy
leakage of the training data. To defend against MI attacks, previous work
utilizes a unilateral dependency optimization strategy, i.e., minimizing the
dependency between inputs (i.e., features) and outputs (i.e., labels) during
training the classifier. However, such a minimization process conflicts with
minimizing the supervised loss that aims to maximize the dependency between
inputs and outputs, causing an explicit trade-off between model robustness
against MI attacks and model utility on classification tasks. In this paper, we
aim to minimize the dependency between the latent representations and the
inputs while maximizing the dependency between latent representations and the
outputs, named a bilateral dependency optimization (BiDO) strategy. In
particular, we use the dependency constraints as a universally applicable
regularizer in addition to commonly used losses for deep neural networks (e.g.,
cross-entropy), which can be instantiated with appropriate dependency criteria
according to different tasks. To verify the efficacy of our strategy, we
propose two implementations of BiDO, by using two different dependency
measures: BiDO with constrained covariance (BiDO-COCO) and BiDO with
Hilbert-Schmidt Independence Criterion (BiDO-HSIC). Experiments show that BiDO
achieves the state-of-the-art defense performance for a variety of datasets,
classifiers, and MI attacks while suffering a minor classification-accuracy
drop compared to the well-trained classifier with no defense, which lights up a
novel road to defend against MI attacks.Comment: Accepted to KDD 2022 (Research Track
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