13,957 research outputs found
full-FORCE: A Target-Based Method for Training Recurrent Networks
Trained recurrent networks are powerful tools for modeling dynamic neural
computations. We present a target-based method for modifying the full
connectivity matrix of a recurrent network to train it to perform tasks
involving temporally complex input/output transformations. The method
introduces a second network during training to provide suitable "target"
dynamics useful for performing the task. Because it exploits the full recurrent
connectivity, the method produces networks that perform tasks with fewer
neurons and greater noise robustness than traditional least-squares (FORCE)
approaches. In addition, we show how introducing additional input signals into
the target-generating network, which act as task hints, greatly extends the
range of tasks that can be learned and provides control over the complexity and
nature of the dynamics of the trained, task-performing network.Comment: 20 pages, 8 figure
A unique model for the variety of multiple populations formation(s) in globular clusters: a temporal sequence
We explain the multiple populations recently found in the 'prototype'
Globular Cluster (GC) NGC 2808 in the framework of the asymptotic giant branch
(AGB) scenario. The chemistry of the five -or more- populations is
approximately consistent with a sequence of star formation events, starting
after the supernovae type II epoch, lasting approximately until the time when
the third dredge up affects the AGB evolution (age ~90-120Myr), and ending when
the type Ia supernovae begin exploding in the cluster, eventually clearing it
from the gas. The formation of the different populations requires episodes of
star formation in AGB gas diluted with different amounts of pristine gas. In
the nitrogen-rich, helium-normal population identified in NGC 2808 by the UV
Legacy Survey of GCs, the nitrogen increase is due to the third dredge up in
the smallest mass AGB ejecta involved in the star formation of this population.
The possibly-iron-rich small population in NGC 2808 may be a result of
contamination by a single type Ia supernova. The NGC 2808 case is used to build
a general framework to understand the variety of 'second generation' stars
observed in GCs. Cluster-to-cluster variations are ascribed to differences in
the effects of the many processes and gas sources which may be involved in the
formation of the second generation. We discuss an evolutionary scheme, based on
pollution by delayed type II supernovae, which accounts for the properties of
s-Fe-anomalous clusters.Comment: 20 pages, 7 figures, in press on MNRA
On Mitigation of Side-Channel Attacks in 3D ICs: Decorrelating Thermal Patterns from Power and Activity
Various side-channel attacks (SCAs) on ICs have been successfully
demonstrated and also mitigated to some degree. In the context of 3D ICs,
however, prior art has mainly focused on efficient implementations of classical
SCA countermeasures. That is, SCAs tailored for up-and-coming 3D ICs have been
overlooked so far. In this paper, we conduct such a novel study and focus on
one of the most accessible and critical side channels: thermal leakage of
activity and power patterns. We address the thermal leakage in 3D ICs early on
during floorplanning, along with tailored extensions for power and thermal
management. Our key idea is to carefully exploit the specifics of material and
structural properties in 3D ICs, thereby decorrelating the thermal behaviour
from underlying power and activity patterns. Most importantly, we discuss
powerful SCAs and demonstrate how our open-source tool helps to mitigate them.Comment: Published in Proc. Design Automation Conference, 201
Optical patterning of trapped charge in nitrogen-doped diamond
The nitrogen-vacancy (NV) centre in diamond is emerging as a promising
platform for solid-state quantum information processing and nanoscale
metrology. Of interest in these applications is the manipulation of the NV
charge, which can be attained by optical excitation. Here we use two-color
optical microscopy to investigate the dynamics of NV photo-ionization, charge
diffusion, and trapping in type-1b diamond. We combine fixed-point laser
excitation and scanning fluorescence imaging to locally alter the concentration
of negatively charged NVs, and to subsequently probe the corresponding
redistribution of charge. We uncover the formation of spatial patterns of
trapped charge, which we qualitatively reproduce via a model of the interplay
between photo-excited carriers and atomic defects. Further, by using the NV as
a probe, we map the relative fraction of positively charged nitrogen upon
localized optical excitation. These observations may prove important to
transporting quantum information between NVs or to developing
three-dimensional, charge-based memories
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