16 research outputs found
FreeREA: Training-Free Evolution-based Architecture Search
In the last decade, most research in Machine Learning contributed to the
improvement of existing models, with the aim of increasing the performance of
neural networks for the solution of a variety of different tasks. However, such
advancements often come at the cost of an increase of model memory and
computational requirements. This represents a significant limitation for the
deployability of research output in realistic settings, where the cost, the
energy consumption, and the complexity of the framework play a crucial role. To
solve this issue, the designer should search for models that maximise the
performance while limiting its footprint. Typical approaches to reach this goal
rely either on manual procedures, which cannot guarantee the optimality of the
final design, or upon Neural Architecture Search algorithms to automatise the
process, at the expenses of extremely high computational time. This paper
provides a solution for the fast identification of a neural network that
maximises the model accuracy while preserving size and computational
constraints typical of tiny devices. Our approach, named FreeREA, is a custom
cell-based evolution NAS algorithm that exploits an optimised combination of
training-free metrics to rank architectures during the search, thus without
need of model training. Our experiments, carried out on the common benchmarks
NAS-Bench-101 and NATS-Bench, demonstrate that i) FreeREA is the first method
able to provide very accurate models in minutes of search time; ii) it
outperforms State of the Art training-based and training-free techniques in all
the datasets and benchmarks considered, and iii) it can easily generalise to
constrained scenarios, representing a competitive solution for fast Neural
Architecture Search in generic constrained applications.Comment: 16 pages, 4 figurre
Entropic Score metric: Decoupling Topology and Size in Training-free NAS
Neural Networks design is a complex and often daunting task, particularly for
resource-constrained scenarios typical of mobile-sized models. Neural
Architecture Search is a promising approach to automate this process, but
existing competitive methods require large training time and computational
resources to generate accurate models. To overcome these limits, this paper
contributes with: i) a novel training-free metric, named Entropic Score, to
estimate model expressivity through the aggregated element-wise entropy of its
activations; ii) a cyclic search algorithm to separately yet synergistically
search model size and topology. Entropic Score shows remarkable ability in
searching for the topology of the network, and a proper combination with
LogSynflow, to search for model size, yields superior capability to completely
design high-performance Hybrid Transformers for edge applications in less than
1 GPU hour, resulting in the fastest and most accurate NAS method for ImageNet
classification.Comment: 10 pages, 3 figure
Adversarial Branch Architecture Search for Unsupervised Domain Adaptation
Unsupervised Domain Adaptation (UDA) is a key issue in visual recognition, as
it allows to bridge different visual domains enabling robust performances in
the real world. To date, all proposed approaches rely on human expertise to
manually adapt a given UDA method (e.g. DANN) to a specific backbone
architecture (e.g. ResNet). This dependency on handcrafted designs limits the
applicability of a given approach in time, as old methods need to be constantly
adapted to novel backbones.
Existing Neural Architecture Search (NAS) approaches cannot be directly
applied to mitigate this issue, as they rely on labels that are not available
in the UDA setting. Furthermore, most NAS methods search for full
architectures, which precludes the use of pre-trained models, essential in a
vast range of UDA settings for reaching SOTA results. To the best of our
knowledge, no prior work has addressed these aspects in the context of NAS for
UDA. Here we tackle both aspects with an Adversarial Branch Architecture Search
for UDA (ABAS): i. we address the lack of target labels by a novel data-driven
ensemble approach for model selection; and ii. we search for an auxiliary
adversarial branch, attached to a pre-trained backbone, which drives the domain
alignment.
We extensively validate ABAS to improve two modern UDA techniques, DANN and
ALDA, on three standard visual recognition datasets (Office31, Office-Home and
PACS). In all cases, ABAS robustly finds the adversarial branch architectures
and parameters which yield best performances.Comment: Accepted at WACV 202
Entropic Score Metric: Decoupling Topology and Size in Training-Free NAS
Neural Networks design is a complex and often daunting
task, particularly for resource-constrained scenarios typi-
cal of mobile-sized models. Neural Architecture Search is
a promising approach to automate this process, but existing
competitive methods require large training time and com-
putational resources to generate accurate models. To over-
come these limits, this paper contributes with: i) a novel
training-free metric, named Entropic Score, to estimate
model expressivity through the aggregated element-wise en-
tropy of its activations; ii) a cyclic search algorithm to sep-
arately yet synergistically search model size and topology.
Entropic Score shows remarkable ability in searching for
the topology of the network, and a proper combination with
LogSynflow, to search for model size, yields superior capa-
bility to completely design high-performance Hybrid Trans-
formers for edge applications in less than 1 GPU hour, re-
sulting in the fastest and most accurate NAS method for Im-
ageNet classification
Photoactive spherical colloids for opal photonic crystals
The synthesis and characterization of submicrometersized
polymer particles, functionalized by different
techniques with fluorescent dyes and featuring tunable
surface charges, are described. Dyes with a polymerizable
moiety were incorporated during emulsifier-free
or seeded emulsion polymerization, whereas nonpolymerizable
dyes were included into preformed
nanoparticles by a swelling and deswelling process.
The particle surface charge was controlled through the
choice of suitable initiators. All the nanoparticles were
successfully used to grow high optical quality opal
photonic crystals by the vertical deposition technique.
Optical characterization of such photonic crystals
pointed out the presence of the optical stop band and
the high-energy van Hove-like structures, both scaling
with the particle diameter according to the scaling
laws of photonic crystals and possessing the expected
angular dispersion. These results are indicative of the
high size uniformity and of the surface quality of the
nanospheres independently on the synthetic method
adopted. Preliminary data seem to suggest some effect
of the opal photonic band structure on the dye fluorescence
spectra
Fluorescent polystyrene photonic crystals self-assembled with water-soluble conjugated polyrotaxanes
We demonstrate control of the photoluminescence spectra and decay rates of water-soluble green-emitting conjugated polyrotaxanes by incorporating them in polystyrene opals with a stop-band spectrally tuned on the rotaxane emission (405–650 nm). We observe a suppression of the luminescence within the photonic stop-band and a corresponding enhancement of the high-energy edge (405–447 nm). Time-resolved measurements reveal a wavelength-dependent modification of the emission lifetime, which is shortened at the high-energy edge (by ∼11%, in the range 405–447 nm), but elongated within the stop-band (by ∼13%, in the range 448–482 nm). We assign both effects to the modification of the density of photonic states induced by the photonic crystal band structure. We propose the growth of fluorescent composite photonic crystals from blends of “solvent-compatible” non-covalently bonded nanosphere-polymer systems as a general method for achieving a uniform distribution of polymeric dopants in three-dimensional self-assembling photonic structures
Ionic Strength Responsive Sulfonated Polystyrene Opals
Stimuli-responsive
photonic crystals (PCs) represent an intriguing class of smart materials
very promising for sensing applications. Here, selective ionic strength
responsive polymeric PCs are reported. They are easily fabricated
by partial sulfonation of polystyrene opals, without using toxic or
expensive monomers and etching steps. The color of the resulting hydrogel-like
ordered structures can be continuously shifted over the entire visible
range (405–760 nm) by changing the content of ions over an
extremely wide range of concentration (from about 70 μM to 4
M). The optical response is completely independent from pH and temperature,
and the initial color can be fully recovered by washing the sulfonated
opals with pure water. These new smart photonic materials could find
important applications as ionic strength sensors for environmental
monitoring as well as for healthcare screening