471 research outputs found
Combating catastrophic forgetting with developmental compression
Generally intelligent agents exhibit successful behavior across problems in
several settings. Endemic in approaches to realize such intelligence in
machines is catastrophic forgetting: sequential learning corrupts knowledge
obtained earlier in the sequence, or tasks antagonistically compete for system
resources. Methods for obviating catastrophic forgetting have sought to
identify and preserve features of the system necessary to solve one problem
when learning to solve another, or to enforce modularity such that minimally
overlapping sub-functions contain task specific knowledge. While successful,
both approaches scale poorly because they require larger architectures as the
number of training instances grows, causing different parts of the system to
specialize for separate subsets of the data. Here we present a method for
addressing catastrophic forgetting called developmental compression. It
exploits the mild impacts of developmental mutations to lessen adverse changes
to previously-evolved capabilities and `compresses' specialized neural networks
into a generalized one. In the absence of domain knowledge, developmental
compression produces systems that avoid overt specialization, alleviating the
need to engineer a bespoke system for every task permutation and suggesting
better scalability than existing approaches. We validate this method on a robot
control problem and hope to extend this approach to other machine learning
domains in the future
Evolving higher-order synergies reveals a trade-off between stability and information integration capacity in complex systems
There has recently been an explosion of interest in how "higher-order"
structures emerge in complex systems. This "emergent" organization has been
found in a variety of natural and artificial systems, although at present the
field lacks a unified understanding of what the consequences of higher-order
synergies and redundancies are for systems. Typical research treat the presence
(or absence) of synergistic information as a dependent variable and report
changes in the level of synergy in response to some change in the system. Here,
we attempt to flip the script: rather than treating higher-order information as
a dependent variable, we use evolutionary optimization to evolve boolean
networks with significant higher-order redundancies, synergies, or statistical
complexity. We then analyse these evolved populations of networks using
established tools for characterizing discrete dynamics: the number of
attractors, average transient length, and Derrida coefficient. We also assess
the capacity of the systems to integrate information. We find that high-synergy
systems are unstable and chaotic, but with a high capacity to integrate
information. In contrast, evolved redundant systems are extremely stable, but
have negligible capacity to integrate information. Finally, the complex systems
that balance integration and segregation (known as Tononi-Sporns-Edelman
complexity) show features of both chaosticity and stability, with a greater
capacity to integrate information than the redundant systems while being more
stable than the random and synergistic systems. We conclude that there may be a
fundamental trade-off between the robustness of a systems dynamics and its
capacity to integrate information (which inherently requires flexibility and
sensitivity), and that certain kinds of complexity naturally balance this
trade-off
Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydro Models
We have performed detailed NLTE spectral synthesis modeling of 2 types of 1-D
hydro models: the very highly parameterized deflagration model W7, and two
delayed detonation models. We find that overall both models do about equally
well at fitting well observed SNe Ia near to maximum light. However, the Si II
6150 feature of W7 is systematically too fast, whereas for the delayed
detonation models it is also somewhat too fast, but significantly better than
that of W7. We find that a parameterized mixed model does the best job of
reproducing the Si II 6150 line near maximum light and we study the differences
in the models that lead to better fits to normal SNe Ia. We discuss what is
required of a hydro model to fit the spectra of observed SNe Ia near maximum
light.Comment: 29 pages, 14 figures, ApJ, in pres
The DICE calibration project: design, characterization, and first results
We describe the design, operation, and first results of a photometric
calibration project, called DICE (Direct Illumination Calibration Experiment),
aiming at achieving precise instrumental calibration of optical telescopes. The
heart of DICE is an illumination device composed of 24 narrow-spectrum,
high-intensity, light-emitting diodes (LED) chosen to cover the
ultraviolet-to-near-infrared spectral range. It implements a point-like source
placed at a finite distance from the telescope entrance pupil, yielding a flat
field illumination that covers the entire field of view of the imager. The
purpose of this system is to perform a lightweight routine monitoring of the
imager passbands with a precision better than 5 per-mil on the relative
passband normalisations and about 3{\AA} on the filter cutoff positions. The
light source is calibrated on a spectrophotometric bench. As our fundamental
metrology standard, we use a photodiode calibrated at NIST. The radiant
intensity of each beam is mapped, and spectra are measured for each LED. All
measurements are conducted at temperatures ranging from 0{\deg}C to 25{\deg}C
in order to study the temperature dependence of the system. The photometric and
spectroscopic measurements are combined into a model that predicts the spectral
intensity of the source as a function of temperature. We find that the
calibration beams are stable at the level -- after taking the slight
temperature dependence of the LED emission properties into account. We show
that the spectral intensity of the source can be characterised with a precision
of 3{\AA} in wavelength. In flux, we reach an accuracy of about 0.2-0.5%
depending on how we understand the off-diagonal terms of the error budget
affecting the calibration of the NIST photodiode. With a routine 60-mn
calibration program, the apparatus is able to constrain the passbands at the
targeted precision levels.Comment: 25 pages, 27 figures, accepted for publication in A&
Acoustic transmission line metamaterial with negative/zero/positive refractive index
A one-dimensional acoustic negative refractive index metamaterial based on the transmission line approach is presented. This structure implements the dual transmission line concept extensively investigated in microwave engineering. It consists of an acoustic waveguide periodically loaded with membranes realizing the function of series ?capacitances? and transversally connected open channels realizing shunt ?inductances.? Transmission line based metamaterials can exhibit a negative refractive index without relying on resonance phenomena, which results in a bandwidth of operation much broader than that observed in resonant devices. In the present case, the negative refractive index band extends over almost one octave, from 0.6 to 1 kHz. The developed structure also exhibits a seamless transition between the negative and positive refractive index bands with a zero index at the transition frequency of 1 kHz. At this frequency, the unit cell is only one tenth of the wavelength. Simple acoustic circuit models are introduced, which allow efficient designs both in terms of dispersion and impedance, while accurately describing all the physical phenomena. Using this approach, a good matching at the structure terminations is achieved. Full-wave simulations, made for a 10-cell-long structure, confirm the good performances in terms of dispersion diagram, Bloch impedance, and reflection and transmission coefficients
Type Ia Supernova Spectral Line Ratios as Luminosity Indicators
Type Ia supernovae have played a crucial role in the discovery of the dark
energy, via the measurement of their light curves and the determination of the
peak brightness via fitting templates to the observed lightcurve shape. Two
spectroscopic indicators are also known to be well correlated with peak
luminosity. Since the spectroscopic luminosity indicators are obtained directly
from observed spectra, they will have different systematic errors than do
measurements using photometry. Additionally, these spectroscopic indicators may
be useful for studies of effects of evolution or age of the SNe Ia progenitor
population. We present several new variants of such spectroscopic indicators
which are easy to automate and which minimize the effects of noise. We show
that these spectroscopic indicators can be measured by proposed JDEM missions
such as SNAP and JEDI.Comment: 50 pages, 19 figures, 24 tables, submitted to Ap
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Towards enduring autonomous robots via embodied energy.
Autonomous robots comprise actuation, energy, sensory and control systems built from materials and structures that are not necessarily designed and integrated for multifunctionality. Yet, animals and other organisms that robots strive to emulate contain highly sophisticated and interconnected systems at all organizational levels, which allow multiple functions to be performed simultaneously. Herein, we examine how system integration and multifunctionality in nature inspires a new paradigm for autonomous robots that we call Embodied Energy. Whereas most untethered robots use batteries to store energy and power their operation, recent advancements in energy-storage techniques enable chemical or electrical energy sources to be embodied directly within the structures and materials used to create robots, rather than requiring separate battery packs. This perspective highlights emerging examples of Embodied Energy in the context of developing autonomous robots
Constraining Type Ia supernova models: SN 2011fe as a test case
The nearby supernova SN 2011fe can be observed in unprecedented detail.
Therefore, it is an important test case for Type Ia supernova (SN Ia) models,
which may bring us closer to understanding the physical nature of these
objects. Here, we explore how available and expected future observations of SN
2011fe can be used to constrain SN Ia explosion scenarios. We base our
discussion on three-dimensional simulations of a delayed detonation in a
Chandrasekhar-mass white dwarf and of a violent merger of two white
dwarfs-realizations of explosion models appropriate for two of the most
widely-discussed progenitor channels that may give rise to SNe Ia. Although
both models have their shortcomings in reproducing details of the early and
near-maximum spectra of SN 2011fe obtained by the Nearby Supernova Factory
(SNfactory), the overall match with the observations is reasonable. The level
of agreement is slightly better for the merger, in particular around maximum,
but a clear preference for one model over the other is still not justified.
Observations at late epochs, however, hold promise for discriminating the
explosion scenarios in a straightforward way, as a nucleosynthesis effect leads
to differences in the 55Co production. SN 2011fe is close enough to be followed
sufficiently long to study this effect.Comment: Accepted for publication in The Astrophysical Journal Letter
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