343 research outputs found
Super-resolution spatial, temporal and functional characterisation of voltage-gated calcium channels involved in exocytosis
The
process
of
information
transfer
between
neurons
or
endocrine
cells
is
one
of
the
most
important,
intricate
and
temporally
precise
processes
in
the
body.
Exocytosis,
which
is
central
to
the
process
of
excitation-‐secretion
coupling,
is
triggered
by
calcium
signalling
through
voltage-‐gated
calcium
channels.
Super-‐resolution
imaging
offers
the
possibility
to
fully
understand
the
spatial
relationship
between
the
SNARE
proteins
involved
in
exocytosis,
vesicles
and
the
associated
voltage-‐gated
calcium
channels.
In
this
thesis
the
focus
is
on
exploring
the
trigger
for
exocytosis,
specifically
the
spatial
and
functional
role
that
voltage-‐gated
calcium
channels
play
in
this
process.
Super-‐
resolution
imaging
techniques
have
been
applied
to
measure
the
interaction
between
Cav2.2
calcium
channels
and
the
syntaxin1a
SNARE
protein,
where
binding
was
found
to
affect
the
overall
channel
distribution.
A
novel
method
of
caged
dye
conjugated
ω-‐
conotoxin
GVIA
binding
was
developed
for
live
cell
single
molecule
imaging
of
Cav2.2
calcium
channels.
An
innovative
approach
to
analyse
channel
functionality
and
the
distribution
of
calcium
events
at
the
plasma
membrane
was
developed
to
create
a
temporal-‐spatial
map
of
calcium
activity
across
the
cell.
These
developments,
combined
with
newly
developed
techniques
in
optical
patching
and
simultaneous
calcium
and
vesicle
imaging
reveal
the
functional
relationship
of
voltage-‐gated
calcium
channel
and
exocytosis
at
unprecedented
spatial
and
temporal
scales
Ericksen-Landau Modular Strain Energies for Reconstructive Phase Transformations in 2D crystals
By using modular functions on the upper complex half-plane, we study a class
of strain energies for crystalline materials whose global invariance originates
from the full symmetry group of the underlying lattice. This follows Ericksen's
suggestion which aimed at extending the Landau-type theories to encompass the
behavior of crystals undergoing structural phase transformation, with twinning,
microstructure formation, and possibly associated plasticity effects. Here we
investigate such Ericksen-Landau strain energies for the modelling of
reconstructive transformations, focusing on the prototypical case of the
square-hexagonal phase change in 2D crystals. We study the bifurcation and
valley-floor network of these potentials, and use one in the simulation of a
quasi-static shearing test. We observe typical effects associated with the
micro-mechanics of phase transformation in crystals, in particular, the bursty
progression of the structural phase change, characterized by intermittent
stress-relaxation through microstructure formation, mediated, in this
reconstructive case, by defect nucleation and movement in the lattice.Comment: 17 pages, 6 figures, links to 4 supplementary video
Cyber Security and Critical Infrastructures
This book contains the manuscripts that were accepted for publication in the MDPI Special Topic "Cyber Security and Critical Infrastructure" after a rigorous peer-review process. Authors from academia, government and industry contributed their innovative solutions, consistent with the interdisciplinary nature of cybersecurity. The book contains 16 articles: an editorial explaining current challenges, innovative solutions, real-world experiences including critical infrastructure, 15 original papers that present state-of-the-art innovative solutions to attacks on critical systems, and a review of cloud, edge computing, and fog's security and privacy issues
Design of self-repairable superhydrophobic and switchable surfaces using colloidal particles
The design of functional materials with complex properties is very important for different applications, such as coatings, microelectronics, biotechnologies and medicine. It is also crucial that such kinds of materials have a long service lifetime. Unfortunately, cracks or other types of damages may occur during everyday use and some parts of the material should be changed for the regeneration of the initial properties. One of the approaches to avoid the replacement is utilization of self-healing materials.
The aim of this thesis was to design a self-repairable material with superhydrophobic and switchable properties using colloidal particles. Specific goals were the synthesis of colloidal particles and the preparation of functional surfaces incorporated with the obtained particles, which would exhibit a repairable switching behavior and repairable superhydrophobicity. In order to achieve these goals, first, methods of preparation of simple and functional colloidal particles were developed. Second, the behavior of particles at surfaces of easy fusible solid materials, namely, paraffin wax or perfluorodecane, was investigated
Secure covert communications over streaming media using dynamic steganography
Streaming technologies such as VoIP are widely embedded into commercial and industrial applications, so it is imperative to address data security issues before the problems get really serious. This thesis describes a theoretical and experimental investigation of secure covert communications over streaming media using dynamic steganography. A covert VoIP communications system was developed in C++ to enable the implementation of the work being carried out.
A new information theoretical model of secure covert communications over streaming media was constructed to depict the security scenarios in streaming media-based steganographic systems with passive attacks. The model involves a stochastic process that models an information source for covert VoIP communications and the theory of hypothesis testing that analyses the adversary‘s detection performance.
The potential of hardware-based true random key generation and chaotic interval selection for innovative applications in covert VoIP communications was explored. Using the read time stamp counter of CPU as an entropy source was designed to generate true random numbers as secret keys for streaming media steganography. A novel interval selection algorithm was devised to choose randomly data embedding locations in VoIP streams using random sequences generated from achaotic process.
A dynamic key updating and transmission based steganographic algorithm that includes a one-way cryptographical accumulator integrated into dynamic key exchange for covert VoIP communications, was devised to provide secure key exchange for covert communications over streaming media. The discrete logarithm problem in mathematics and steganalysis using t-test revealed the algorithm has the advantage of being the most solid method of key distribution over a public channel.
The effectiveness of the new steganographic algorithm for covert communications over streaming media was examined by means of security analysis, steganalysis using non parameter Mann-Whitney-Wilcoxon statistical testing, and performance and robustness measurements. The algorithm achieved the average data embedding rate of 800 bps, comparable to other related algorithms. The results indicated that the algorithm has no or little impact on real-time VoIP communications in terms of speech quality (< 5% change in PESQ with hidden data), signal distortion (6% change in SNR after steganography) and imperceptibility, and it is more secure and effective in addressing the security problems than other related algorithms
Permutationally Invariant Networks for Enhanced Sampling (PINES): Discovery of Multi-Molecular and Solvent-Inclusive Collective Variables
The typically rugged nature of molecular free energy landscapes can frustrate
efficient sampling of the thermodynamically relevant phase space due to the
presence of high free energy barriers. Enhanced sampling techniques can improve
phase space exploration by accelerating sampling along particular collective
variables (CVs). A number of techniques exist for data-driven discovery of CVs
parameterizing the important large scale motions of the system. A challenge to
CV discovery is learning CVs invariant to symmetries of the molecular system,
frequently rigid translation, rigid rotation, and permutational relabeling of
identical particles. Of these, permutational invariance have proved a
persistent challenge in frustrating the the data-driven discovery of
multi-molecular CVs in systems of self-assembling particles and
solvent-inclusive CVs for solvated systems. In this work, we integrate
Permutation Invariant Vector (PIV) featurizations with autoencoding neural
networks to learn nonlinear CVs invariant to translation, rotation, and
permutation, and perform interleaved rounds of CV discovery and enhanced
sampling to iteratively expand sampling of configurational phase space and
obtain converged CVs and free energy landscapes. We demonstrate the
Permutationally Invariant Network for Enhanced Sampling (PINES) approach in
applications to the self-assembly of a 13-atom Argon cluster,
association/dissociation of a NaCl ion pair in water, and hydrophobic collapse
of a C45H92 n-pentatetracontane polymer chain. We make the approach freely
available as a new module within the PLUMED2 enhanced sampling libraries
Soft Biometric Analysis: MultiPerson and RealTime Pedestrian Attribute Recognition in Crowded Urban Environments
Traditionally, recognition systems were only based on human hard biometrics. However,
the ubiquitous CCTV cameras have raised the desire to analyze human biometrics from
far distances, without people attendance in the acquisition process. Highresolution
face closeshots
are rarely available at far distances such that facebased
systems cannot
provide reliable results in surveillance applications. Human soft biometrics such as body
and clothing attributes are believed to be more effective in analyzing human data collected
by security cameras.
This thesis contributes to the human soft biometric analysis in uncontrolled environments
and mainly focuses on two tasks: Pedestrian Attribute Recognition (PAR) and person reidentification
(reid).
We first review the literature of both tasks and highlight the history
of advancements, recent developments, and the existing benchmarks. PAR and person reid
difficulties are due to significant distances between intraclass
samples, which originate
from variations in several factors such as body pose, illumination, background, occlusion,
and data resolution. Recent stateoftheart
approaches present endtoend
models that
can extract discriminative and comprehensive feature representations from people. The
correlation between different regions of the body and dealing with limited learning data
is also the objective of many recent works. Moreover, class imbalance and correlation
between human attributes are specific challenges associated with the PAR problem.
We collect a large surveillance dataset to train a novel gender recognition model suitable
for uncontrolled environments. We propose a deep residual network that extracts several
posewise
patches from samples and obtains a comprehensive feature representation. In
the next step, we develop a model for multiple attribute recognition at once. Considering
the correlation between human semantic attributes and class imbalance, we respectively
use a multitask
model and a weighted loss function. We also propose a multiplication
layer on top of the backbone features extraction layers to exclude the background features
from the final representation of samples and draw the attention of the model to the
foreground area.
We address the problem of person reid
by implicitly defining the receptive fields of
deep learning classification frameworks. The receptive fields of deep learning models
determine the most significant regions of the input data for providing correct decisions.
Therefore, we synthesize a set of learning data in which the destructive regions (e.g.,
background) in each pair of instances are interchanged. A segmentation module
determines destructive and useful regions in each sample, and the label of synthesized
instances are inherited from the sample that shared the useful regions in the synthesized
image. The synthesized learning data are then used in the learning phase and help
the model rapidly learn that the identity and background regions are not correlated.
Meanwhile, the proposed solution could be seen as a data augmentation approach that
fully preserves the label information and is compatible with other data augmentation
techniques.
When reid
methods are learned in scenarios where the target person appears with identical garments in the gallery, the visual appearance of clothes is given the most
importance in the final feature representation. Clothbased
representations are not
reliable in the longterm
reid
settings as people may change their clothes. Therefore,
developing solutions that ignore clothing cues and focus on identityrelevant
features are
in demand. We transform the original data such that the identityrelevant
information of
people (e.g., face and body shape) are removed, while the identityunrelated
cues (i.e.,
color and texture of clothes) remain unchanged. A learned model on the synthesized
dataset predicts the identityunrelated
cues (shortterm
features). Therefore, we train a
second model coupled with the first model and learns the embeddings of the original data
such that the similarity between the embeddings of the original and synthesized data is
minimized. This way, the second model predicts based on the identityrelated
(longterm)
representation of people.
To evaluate the performance of the proposed models, we use PAR and person reid
datasets, namely BIODI, PETA, RAP, Market1501,
MSMTV2,
PRCC, LTCC, and MIT
and compared our experimental results with stateoftheart
methods in the field.
In conclusion, the data collected from surveillance cameras have low resolution, such
that the extraction of hard biometric features is not possible, and facebased
approaches
produce poor results. In contrast, soft biometrics are robust to variations in data quality.
So, we propose approaches both for PAR and person reid
to learn discriminative features
from each instance and evaluate our proposed solutions on several publicly available
benchmarks.This thesis was prepared at the University of Beria Interior, IT Instituto de Telecomunicações, Soft Computing and Image Analysis Laboratory (SOCIA Lab), Covilhã Delegation, and was submitted to the University of Beira Interior for defense in a public examination session
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