2,306 research outputs found
Stoichiometry determination of chalcogenide superlattices by means of X-ray diffraction and its limits
In this paper we explore the potential of stoichiometry determination for
chalcogenide superlattices, promising candidates for next-generation
phase-change memory, via X-ray diffraction. To this end, a set of epitaxial
GeTe/Sb2Te3 superlattice samples with varying layer thicknesses is
sputter-deposited. Kinematical scattering theory is employed to link the
average composition with the diffraction features. The observed lattice
constants of the superlattice reference unit cell follow Vegard's law, enabling
a straight-forward and non-destructive stoichiometry determination.Comment: physica status solidi (RRL) - Rapid Research Letters (2019
Learning not to learn: Nature versus nurture in silico
Animals are equipped with a rich innate repertoire of sensory, behavioral and
motor skills, which allows them to interact with the world immediately after
birth. At the same time, many behaviors are highly adaptive and can be tailored
to specific environments by means of learning. In this work, we use
mathematical analysis and the framework of meta-learning (or 'learning to
learn') to answer when it is beneficial to learn such an adaptive strategy and
when to hard-code a heuristic behavior. We find that the interplay of
ecological uncertainty, task complexity and the agents' lifetime has crucial
effects on the meta-learned amortized Bayesian inference performed by an agent.
There exist two regimes: One in which meta-learning yields a learning algorithm
that implements task-dependent information-integration and a second regime in
which meta-learning imprints a heuristic or 'hard-coded' behavior. Further
analysis reveals that non-adaptive behaviors are not only optimal for aspects
of the environment that are stable across individuals, but also in situations
where an adaptation to the environment would in fact be highly beneficial, but
could not be done quickly enough to be exploited within the remaining lifetime.
Hard-coded behaviors should hence not only be those that always work, but also
those that are too complex to be learned within a reasonable time frame
Lottery Tickets in Evolutionary Optimization: On Sparse Backpropagation-Free Trainability
Is the lottery ticket phenomenon an idiosyncrasy of gradient-based training
or does it generalize to evolutionary optimization? In this paper we establish
the existence of highly sparse trainable initializations for evolution
strategies (ES) and characterize qualitative differences compared to gradient
descent (GD)-based sparse training. We introduce a novel signal-to-noise
iterative pruning procedure, which incorporates loss curvature information into
the network pruning step. This can enable the discovery of even sparser
trainable network initializations when using black-box evolution as compared to
GD-based optimization. Furthermore, we find that these initializations encode
an inductive bias, which transfers across different ES, related tasks and even
to GD-based training. Finally, we compare the local optima resulting from the
different optimization paradigms and sparsity levels. In contrast to GD, ES
explore diverse and flat local optima and do not preserve linear mode
connectivity across sparsity levels and independent runs. The results highlight
qualitative differences between evolution and gradient-based learning dynamics,
which can be uncovered by the study of iterative pruning procedures.Comment: 13 pages, 11 figures, International Conference on Machine Learning
(ICML) 202
Disaggregation by State Inference A Probabilistic Framework For Non-Intrusive Load Monitoring
Non-intrusive load monitoring (NILM), the problem of disaggregating whole home power measurements into single-appliance measurements, has received increasing attention from the academic community because of its energy saving potentials, however the majority of NILM approaches are either variants of event-based or event-less disaggregation. Event-based approaches are able to capture much information about the transient behavior of appliances but suffer from error-propagation problems whereas event-less approaches are lessprone to error-propagation problems but can only incorporate transient information to a small degree. On top of that inference techniques for event-less approaches are either computationally expensive, do not allow to trade off computational time for approximation accuracy or are prone to local minima. This work will contribute three-fold: first an automated way to infer ground truth from single appliance readings is introduced, second an augmentation for event-less approaches is introduced that allows to capture side-channel as well as transient information of change-points, third an inference technique is presented that allows to control the trade-off between computational expense and accuracy. Ultimately, this work will try to put the NILM problem into a probabilistic framework that allows for closing feedback loops between the different stages of event-based NILM approaches, effectively bridging event-less and event-based approaches. The performance of the inference technique is evaluated on a synthetic data set and compared to state-of-the-art approaches. Then the hypothesis that incorporating transient information increases the disaggregation performance is tested on a real-life data set
On Lottery Tickets and Minimal Task Representations in Deep Reinforcement Learning
The lottery ticket hypothesis questions the role of overparameterization in
supervised deep learning. But how is the performance of winning lottery tickets
affected by the distributional shift inherent to reinforcement learning
problems? In this work, we address this question by comparing sparse agents who
have to address the non-stationarity of the exploration-exploitation problem
with supervised agents trained to imitate an expert. We show that feed-forward
networks trained with behavioural cloning compared to reinforcement learning
can be pruned to higher levels of sparsity without performance degradation.
This suggests that in order to solve the RL-specific distributional shift
agents require more degrees of freedom. Using a set of carefully designed
baseline conditions, we find that the majority of the lottery ticket effect in
both learning paradigms can be attributed to the identified mask rather than
the weight initialization. The input layer mask selectively prunes entire input
dimensions that turn out to be irrelevant for the task at hand. At a moderate
level of sparsity the mask identified by iterative magnitude pruning yields
minimal task-relevant representations, i.e., an interpretable inductive bias.
Finally, we propose a simple initialization rescaling which promotes the robust
identification of sparse task representations in low-dimensional control tasks.Comment: 20 pages, 15 figure
Programming of Intelligent Service Robots with the Process Model “FRIEND::Process” and Configurable Task-Knowledge
Modeling Appropriate Language in Argumentation
Online discussion moderators must make ad-hoc decisions about whether the
contributions of discussion participants are appropriate or should be removed
to maintain civility. Existing research on offensive language and the resulting
tools cover only one aspect among many involved in such decisions. The question
of what is considered appropriate in a controversial discussion has not yet
been systematically addressed. In this paper, we operationalize appropriate
language in argumentation for the first time. In particular, we model
appropriateness through the absence of flaws, grounded in research on argument
quality assessment, especially in aspects from rhetoric. From these, we derive
a new taxonomy of 14 dimensions that determine inappropriate language in online
discussions. Building on three argument quality corpora, we then create a
corpus of 2191 arguments annotated for the 14 dimensions. Empirical analyses
support that the taxonomy covers the concept of appropriateness
comprehensively, showing several plausible correlations with argument quality
dimensions. Moreover, results of baseline approaches to assessing
appropriateness suggest that all dimensions can be modeled computationally on
the corpus
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