5,642 research outputs found
Sliced Wasserstein Distance for Learning Gaussian Mixture Models
Gaussian mixture models (GMM) are powerful parametric tools with many
applications in machine learning and computer vision. Expectation maximization
(EM) is the most popular algorithm for estimating the GMM parameters. However,
EM guarantees only convergence to a stationary point of the log-likelihood
function, which could be arbitrarily worse than the optimal solution. Inspired
by the relationship between the negative log-likelihood function and the
Kullback-Leibler (KL) divergence, we propose an alternative formulation for
estimating the GMM parameters using the sliced Wasserstein distance, which
gives rise to a new algorithm. Specifically, we propose minimizing the
sliced-Wasserstein distance between the mixture model and the data distribution
with respect to the GMM parameters. In contrast to the KL-divergence, the
energy landscape for the sliced-Wasserstein distance is more well-behaved and
therefore more suitable for a stochastic gradient descent scheme to obtain the
optimal GMM parameters. We show that our formulation results in parameter
estimates that are more robust to random initializations and demonstrate that
it can estimate high-dimensional data distributions more faithfully than the EM
algorithm
Adversarial Example Detection and Classification With Asymmetrical Adversarial Training
The vulnerabilities of deep neural networks against adversarial examples have
become a significant concern for deploying these models in sensitive domains.
Devising a definitive defense against such attacks is proven to be challenging,
and the methods relying on detecting adversarial samples are only valid when
the attacker is oblivious to the detection mechanism. In this paper we first
present an adversarial example detection method that provides performance
guarantee to norm constrained adversaries. The method is based on the idea of
training adversarial robust subspace detectors using asymmetrical adversarial
training (AAT). The novel AAT objective presents a minimax problem similar to
that of GANs; it has the same convergence property, and consequently supports
the learning of class conditional distributions. We first demonstrate that the
minimax problem could be reasonably solved by PGD attack, and then use the
learned class conditional generative models to define generative
detection/classification models that are both robust and more interpretable. We
provide comprehensive evaluations of the above methods, and demonstrate their
competitive performances and compelling properties on adversarial detection and
robust classification problems.Comment: ICLR 202
Non-deterministic approximation of photon number discriminating detectors using non-discriminating detectors
We present a scheme for non-deterministically approximating photon number
resolving detectors using non-discriminating detectors. The model is simple in
construction and employs very few physical resources. Despite its
non-determinism, the proposal may nonetheless be suitable for use in some
quantum optics experiments in which non-determinism can be tolerated. We
analyze the detection scheme in the context of an optical implementation of the
controlled-NOT gate, an inherently non-deterministic device. This allows the
gate's success probability to be traded away for improved gate fidelity,
assuming high efficiency detectors. The scheme is compared to two other
proposals, both deterministic, for approximating discriminating detectors using
non-discriminating detectors: the cascade and time division multiplexing
schemes.Comment: 5 pages, 7 figures (published version
Habitat width along a latitudinal gradient
We use the Chowdhury ecosystem model, one of the most complex agent-based
ecological models, to test the latitude-niche breadth hypothesis, with regard
to habitat width, i.e., whether tropical species generally have narrower
habitats than high latitude ones. Application of the model has given realistic
results in previous studies on latitudinal gradients in species diversity and
Rapoport's rule. Here we show that tropical species with sufficient vagility
and time to spread into adjacent habitats, tend to have wider habitats than
high latitude ones, contradicting the latitude-niche breadth hypothesis.Comment: 13 pages including all figures, draft for a biology journa
Bypassing the structural bottleneck in the ultrafast melting of electronic order
The emergent properties of quantum materials, such as symmetry-broken phases
and associated spectral gaps, can be effectively manipulated by ultrashort
photon pulses. Impulsive optical excitation generally results in a complex
non-equilibrium electron and lattice dynamics that involves multiple processes
on distinct timescales, and a common conception is that for times shorter than
about 100 fs the gap in the electronic spectrum is not seriously affected by
lattice vibrations. Here, we directly monitor the photo-induced collapse of the
spectral gap in a canonical charge-density-wave material, blue bronze
Rb0.3MoO3. We find that ultra-fast (about 60 fs) vibrational disordering due to
efficient hot-electron energy dissipation quenches the gap significantly faster
than the typical structural bottleneck time corresponding to one half-cycle
oscillation (about 315 fs) of the coherent charge-density-wave amplitude mode.
This result not only demonstrates the importance of incoherent lattice motion
in the photo-induced quenching of electronic order, but also resolves the
perennial debate about the nature of the spectral gap in a coupled
electron-lattice system
COMPLIANCE TESTING OF IOWA’S SKID-MOUNTED SIGN DEVICE
A wide variety of traffic control devices are used in work zones, some of which are nont ormally found on the roadside or in the traveled way outsideofthe work zones. These devices are used to enhance the safety of the work zones by controlling the traffic through these areas. Due to the placement of the traffic control devices, the devices themselves may be potentially hazardous to both workers and errant vehicles. The impact performance of many work zone traffic control devices is mainly unknown and to date limited crash testing has been conducted under the criteria of National Cooperative Highway Research Program (NCHRP) Report No. 350, Recommended Procedures for the Safety Performance Evaluation of Highway Features.
The objective of the study was to evaluatethe safety performance of existing skid-mounted sign supports through full- scale crash testing. Two full-scale crash tests were conducted on skid-mounted sign supports to determine their safety performance according to the Test Level 3 (TL-3) criteria set forth in the NCHRP Report No. 350. The safety performancevaluations indicate that these skid-mounted sign supports did not perform satisfactorily in the full-scale crash tests. The results of the crash tests were documented, and conclusions and recommendations pertaining tothe safety performance of the existing work zone traffic control devices were made
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