890 research outputs found
Blockout: Dynamic Model Selection for Hierarchical Deep Networks
Most deep architectures for image classification--even those that are trained
to classify a large number of diverse categories--learn shared image
representations with a single model. Intuitively, however, categories that are
more similar should share more information than those that are very different.
While hierarchical deep networks address this problem by learning separate
features for subsets of related categories, current implementations require
simplified models using fixed architectures specified via heuristic clustering
methods. Instead, we propose Blockout, a method for regularization and model
selection that simultaneously learns both the model architecture and
parameters. A generalization of Dropout, our approach gives a novel
parametrization of hierarchical architectures that allows for structure
learning via back-propagation. To demonstrate its utility, we evaluate Blockout
on the CIFAR and ImageNet datasets, demonstrating improved classification
accuracy, better regularization performance, faster training, and the clear
emergence of hierarchical network structures
Glassiness and constrained dynamics of a short-range non-disordered spin model
We study the low temperature dynamics of a two dimensional short-range spin
system with uniform ferromagnetic interactions, which displays glassiness at
low temperatures despite the absence of disorder or frustration. The model has
a dual description in terms of free defects subject to dynamical constraints,
and is an explicit realization of the ``hierarchically constrained dynamics''
scenario for glassy systems. We give a number of exact results for the statics
of the model, and study in detail the dynamical behaviour of one-time and
two-time quantities. We also consider the role played by the configurational
entropy, which can be computed exactly, in the relation between fluctuations
and response.Comment: 10 pages, 9 figures; minor changes, references adde
Sub 20 nm Silicon Patterning and Metal Lift-Off Using Thermal Scanning Probe Lithography
The most direct definition of a patterning process' resolution is the
smallest half-pitch feature it is capable of transferring onto the substrate.
Here we demonstrate that thermal Scanning Probe Lithography (t-SPL) is capable
of fabricating dense line patterns in silicon and metal lift-off features at
sub 20 nm feature size. The dense silicon lines were written at a half pitch of
18.3 nm to a depth of 5 nm into a 9 nm polyphthalaldehyde thermal imaging layer
by t-SPL. For processing we used a three-layer stack comprising an evaporated
SiO2 hardmask which is just 2-3 nm thick. The hardmask is used to amplify the
pattern into a 50 nm thick polymeric transfer layer. The transfer layer
subsequently serves as an etch mask for transfer into silicon to a nominal
depth of 60 nm. The line edge roughness (3 sigma) was evaluated to be less than
3 nm both in the transfer layer and in silicon. We also demonstrate that a
similar three-layer stack can be used for metal lift-off of high resolution
patterns. A device application is demonstrated by fabricating 50 nm half pitch
dense nickel contacts to an InAs nanowire.Comment: 7 pages, 5 figures, to be published in JVST
Tweed in Martensites: A Potential New Spin Glass
We've been studying the ``tweed'' precursors above the martensitic transition
in shape--memory alloys. These characteristic cross--hatched modulations occur
for hundreds of degrees above the first--order shape--changing transition. Our
two--dimensional model for this transition, in the limit of infinite elastic
anisotropy, can be mapped onto a spin--glass Hamiltonian in a random field. We
suggest that the tweed precursors are a direct analogy of the spin--glass
phase. The tweed is intermediate between the high--temperature cubic phase and
the low--temperature martensitic phase in the same way as the spin--glass phase
can be intermediate between ferromagnet and antiferromagnet.Comment: 18 pages and four figures (included
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