62,897 research outputs found
Structured Dropout for Weak Label and Multi-Instance Learning and Its Application to Score-Informed Source Separation
Many success stories involving deep neural networks are instances of
supervised learning, where available labels power gradient-based learning
methods. Creating such labels, however, can be expensive and thus there is
increasing interest in weak labels which only provide coarse information, with
uncertainty regarding time, location or value. Using such labels often leads to
considerable challenges for the learning process. Current methods for
weak-label training often employ standard supervised approaches that
additionally reassign or prune labels during the learning process. The
information gain, however, is often limited as only the importance of labels
where the network already yields reasonable results is boosted. We propose
treating weak-label training as an unsupervised problem and use the labels to
guide the representation learning to induce structure. To this end, we propose
two autoencoder extensions: class activity penalties and structured dropout. We
demonstrate the capabilities of our approach in the context of score-informed
source separation of music
Polarization of electric field noise near metallic surfaces
Electric field noise in proximity to metallic surfaces is a poorly understood
phenomenon that appears in different areas of physics. Trapped ion quantum
information processors are particular susceptible to this noise, leading to
motional decoherence which ultimately limits the fidelity of quantum
operations. On the other hand they present an ideal tool to study this effect,
opening new possibilities in surface science. In this work we analyze and
measure the polarization of the noise field in a micro-fabricated ion trap for
various noise sources. We find that technical noise sources and noise emanating
directly from the surface give rise to different degrees of polarization which
allows us to differentiate between the two noise sources. Based on this, we
demonstrate a method to infer the magnitude of surface noise in the presence of
technical noise
Slow waves in locally resonant metamaterials line defect waveguides
In the past decades, many efforts have been devoted to the temporal
manipulation of waves, especially focusing on slowing down their propagation.
In electromagnetism, from microwave to optics, as well as in acoustics or for
elastic waves, slow wave propagation indeed largely benefits both applied and
fundamental physics. It is for instance essential in analog signal computing
through the design of components such as delay lines and buffers, and it is one
of the prerequisite for increased wave/matter interactions. Despite the
interest of a broad community, researches have mostly been conducted in optics
along with the development of wavelength scaled structured composite media,
that appear promising candidates for compact slow light components. Yet their
minimum structural scale prevents them from being transposed to lower
frequencies where wavelengths range from sub-millimeter to meters. In this
article, we propose to overcome this limitation thanks to the deep
sub-wavelength scale of locally resonant metamaterials. In our approach,
implemented here in the microwave regime, we show that introducing coupled
resonant defects in such composite media allows the creation of deep
sub-wavelength waveguides. We experimentally demonstrate that waves, while
propagating in such waveguides, exhibit largely reduced group velocities. We
qualitatively explain the mechanism underlying this slow wave propagation and
first experimentally demonstrate, then numerically verify, how it can be taken
advantage of to tune the velocity, achieving group indices ng as high as 227
over relatively large bandwidths. We conclude by highlighting the three
beneficial consequences of our line defect slow wave waveguides in locally
resonant metamaterials: the deep sub-wavelength scale, the very large group
indices and the fact that slow wave propagation does not occur at the expense
of drastic bandwidth reductions
Fast, scalable, Bayesian spike identification for multi-electrode arrays
We present an algorithm to identify individual neural spikes observed on
high-density multi-electrode arrays (MEAs). Our method can distinguish large
numbers of distinct neural units, even when spikes overlap, and accounts for
intrinsic variability of spikes from each unit. As MEAs grow larger, it is
important to find spike-identification methods that are scalable, that is, the
computational cost of spike fitting should scale well with the number of units
observed. Our algorithm accomplishes this goal, and is fast, because it
exploits the spatial locality of each unit and the basic biophysics of
extracellular signal propagation. Human intervention is minimized and
streamlined via a graphical interface. We illustrate our method on data from a
mammalian retina preparation and document its performance on simulated data
consisting of spikes added to experimentally measured background noise. The
algorithm is highly accurate
Transient LTRE analysis reveals the demographic and trait-mediated processes that buffer population growth.
Temporal variation in environmental conditions affects population growth directly via its impact on vital rates, and indirectly through induced variation in demographic structure and phenotypic trait distributions. We currently know very little about how these processes jointly mediate population responses to their environment. To address this gap, we develop a general transient life table response experiment (LTRE) which partitions the contributions to population growth arising from variation in (1) survival and reproduction, (2) demographic structure, (3) trait values and (4) climatic drivers. We apply the LTRE to a population of yellow-bellied marmots (Marmota flaviventer) to demonstrate the impact of demographic and trait-mediated processes. Our analysis provides a new perspective on demographic buffering, which may be a more subtle phenomena than is currently assumed. The new LTRE framework presents opportunities to improve our understanding of how trait variation influences population dynamics and adaptation in stochastic environments
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