359 research outputs found
Determination of complex absorbing potentials from the electron self-energy
The electronic conductance of a molecule making contact to electrodes is
determined by the coupling of discrete molecular states to the continuum
electrode density of states. Interactions between bound states and continua can
be modeled exactly by using the (energy-dependent) self-energy, or
approximately by using a complex potential. We discuss the relation between the
two approaches and give a prescription for using the self-energy to construct
an energy-independent, non-local, complex potential. We apply our scheme to
studying single-electron transmission in an atomic chain, obtaining excellent
agreement with the exact result. Our approach allows us to treat
electron-reservoir couplings independent of single electron energies, allowing
for the definition of a one-body operator suitable for inclusion into
correlated electron transport calculations.Comment: 11 pages, 8 figures; to be published in the J. Chem. Phy
Online Extraction and Single Trial Analysis of Regions Contributing to Erroneous Feedback Detection
International audienceUnderstanding how the brain processes errors is an essential and active field of neuroscience. Real time extraction and analysis of error signals provide an innovative method of assessing how individuals perceive ongoing interactions without recourse to overt behaviour. This area of research is critical in modern BrainâComputer Interface (BCI) design, but may also open fruitful perspectives in cognitive neuroscience research. In this context, we sought to determine whether we can extract discriminatory error-related activity in the source space, online, and on a trial by trial basis from electroencephalography data recorded during motor imagery. Using a data driven approach, based on interpretable inverse solution algorithms, we assessed the extent to which automatically extracted error-related activity was physiologically and functionally interpretable according to performance monitoring literature. The applicability of inverse solution based methods for automatically extracting error signals, in the presence of noise generated by motor imagery, was validated by simulation. Representative regions of interest, outlining the primary generators contributing to classification, were found to correspond closely to networks involved in error detection and performance monitoring. We observed discriminative activity in non-frontal areas, demonstrating that areas outside of the medial frontal cortex can contribute to the classification of error feedback activity
Scaling of critical wave functions at topological Anderson transitions in one dimension
Topological Anderson transitions, which are direct phase transitions between topologically distinct Anderson localized phases, allow for criticality in one-dimensional disordered systems. We analyze the statistical properties of an ensemble of critical wave functions at such transitions. We find that the local moments are strongly inhomogeneous, with significant amplification towards the edges of the system. In particular, we obtain an analytic expression for the spatial profile of the local moments, which is valid at all topological Anderson transitions in one dimension, as we verify by direct comparison with numerical simulations of various lattice models
Impact of alloy disorder on the band structure of compressively strained GaBiAs
The incorporation of bismuth (Bi) in GaAs results in a large reduction of the
band gap energy (E) accompanied with a large increase in the spin-orbit
splitting energy (), leading to the condition that
which is anticipated to reduce so-called CHSH Auger
recombination losses whereby the energy and momentum of a recombining
electron-hole pair is given to a second hole which is excited into the
spin-orbit band. We theoretically investigate the electronic structure of
experimentally grown GaBiAs samples on (100) GaAs substrates by
directly comparing our data with room temperature photo-modulated reflectance
(PR) measurements. Our atomistic theoretical calculations, in agreement with
the PR measurements, confirm that E is equal to for
9. We then theoretically probe the inhomogeneous
broadening of the interband transition energies as a function of the alloy
disorder. The broadening associated with spin-split-off transitions arises from
conventional alloy effects, while the behaviour of the heavy-hole transitions
can be well described using a valence band-anticrossing model. We show that for
the samples containing 8.5% and 10.4% Bi the difficulty in identifying a clear
light-hole-related transition energy from the measured PR data is due to the
significant broadening of the host matrix light-hole states as a result of the
presence of a large number of Bi resonant states in the same energy range and
disorder in the alloy. We further provide quantitative estimates of the impact
of supercell size and the assumed random distribution of Bi atoms on the
interband transition energies in GaBiAs. Our calculations support
a type-I band alignment at the GaBiAs/GaAs interface, consistent
with recent experimental findings
A multi-wavelength discriminating sensor with a wireless mote interface for aquatic pollution monitoring
peer-reviewedThe system presented in this paper demonstrates how a novel fibre optic based sensing platform, capable of detecting minute changes in the level of impurity in a liquid, can be incorporated onto a Mote based platform enabling real time monitoring of a body of water. How these features can be used to detect a representative sample of chlorophyll within a aquatic environment, will be demonstrated. Systems currently deployed worldwide include satellite mapping technology and high cost water monitoring platforms. Growing international emphasis on the management of water quality is giving rise to an expansion of the international market for novel robust, miniaturized, intelligent water monitoring systems capable of measuring local environmentally detrimental events such as localised small scale chemical pollution.PUBLISHEDpeer-reviewe
Local Model Reconstruction Attacks in Federated Learning and their Uses
In this paper, we initiate the study of local model reconstruction attacks
for federated learning, where a honest-but-curious adversary eavesdrops the
messages exchanged between a targeted client and the server, and then
reconstructs the local/personalized model of the victim. The local model
reconstruction attack allows the adversary to trigger other classical attacks
in a more effective way, since the local model only depends on the client's
data and can leak more private information than the global model learned by the
server. Additionally, we propose a novel model-based attribute inference attack
in federated learning leveraging the local model reconstruction attack. We
provide an analytical lower-bound for this attribute inference attack.
Empirical results using real world datasets confirm that our local
reconstruction attack works well for both regression and classification tasks.
Moreover, we benchmark our novel attribute inference attack against the
state-of-the-art attacks in federated learning. Our attack results in higher
reconstruction accuracy especially when the clients' datasets are
heterogeneous. Our work provides a new angle for designing powerful and
explainable attacks to effectively quantify the privacy risk in FL
Optimizing P300-speller sequences by RIP-ping groups apart
International audienceSo far P300-speller design has put very little emphasis on the design of optimized flash patterns, a surprising fact given the importance of the sequence of flashes on the selection outcome. Previous work in this domain has consisted in studying consecutive flashes, to prevent the same letter or its neighbors from flashing consecutively. To this effect, the flashing letters form more random groups than the original row-column sequences for the P300 paradigm, but the groups remain fixed across repetitions. This has several important consequences, among which a lack of discrepancy between the scores of the different letters. The new approach proposed in this paper accumulates evidence for individual elements, and optimizes the sequences by relaxing the constraint that letters should belong to fixed groups across repetitions. The method is inspired by the theory of Restricted Isometry Property matrices in Compressed Sensing, and it can be applied to any display grid size, and for any target flash frequency. This leads to P300 sequences which are shown here to perform significantly better than the state of the art, in simulations and online tests
Automated on-disc total RNA extraction from whole blood towards point-of-care for early-stage diagnostics
We present a novel integrated, centrifugo-pneumatic
micro-homogenizer (âÎŒHomogenizerâ) for automated
sample preparation and total RNA extraction from whole
blood. Using a Trizol based protocol, this novel
ÎŒHomogenizer efficiently lyses whole blood spiked with
E. coli, retains the organic-mixed fraction and yields the
aqueous phase with the total RNA content. By the
interplay of microfluidic design and a protocol of
rotational frequencies, we concatenate (and parallelize) a
sequence of five subsequent liquid handling operations
that complete in less than 10 minutes. A comparison of
the total nucleotide content yields similar performance as
conventional, essentially manual off-disc sample
preparation methods
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