135 research outputs found
Macroscopic Dynamics of Neural Networks with Heterogeneous Spiking Thresholds
Mean-field theory links the physiological properties of individual neurons to
the emergent dynamics of neural population activity. These models provide an
essential tool for studying brain function at different scales; however, for
their application to neural populations on large scale, they need to account
for differences between distinct neuron types. The Izhikevich single neuron
model can account for a broad range of different neuron types and spiking
patterns, thus rendering it an optimal candidate for a mean-field theoretic
treatment of brain dynamics in heterogeneous networks. Here, we derive the
mean-field equations for networks of all-to-all coupled Izhikevich neurons with
heterogeneous spiking thresholds. Using methods from bifurcation theory, we
examine the conditions under which the mean-field theory accurately predicts
the dynamics of the Izhikevich neuron network. To this end, we focus on three
important features of the Izhikevich model that are subject here to simplifying
assumptions: (i) spike-frequency adaptation, (ii) the spike reset conditions,
and (iii) the distribution of single-cell spike thresholds across neurons.
Our results indicate that, while the mean-field model is not an exact model
of the Izhikevich network dynamics, it faithfully captures its different
dynamic regimes and phase transitions. We thus present a mean-field model that
can represent different neuron types and spiking dynamics. The model is
comprised of biophysical state variables and parameters, incorporates realistic
spike resetting conditions, and accounts for heterogeneity in neural spiking
thresholds. These features allow for a broad applicability of the model as well
as for a direct comparison to experimental data.Comment: 13 pages, 4 figure
Mean-field approximations of networks of spiking neurons with short-term synaptic plasticity
Low-dimensional descriptions of neural network dynamics are an effective tool
for bridging different scales of organization of brain structure and function.
Recent advances in deriving mean-field descriptions for networks of coupled
oscillators have sparked the development of a new generation of neural mass
models. Of notable interest are mean-field descriptions of all-to-all coupled
quadratic integrate-and-fire (QIF) neurons, which have already seen numerous
extensions and applications. These extensions include different forms of
short-term adaptation (STA) considered to play an important role in generating
and sustaining dynamic regimes of interest in the brain. It is an open
question, however, whether the incorporation of pre-synaptic forms of synaptic
plasticity driven by single neuron activity would still permit the derivation
of mean-field equations using the same method. Here, we discuss this problem
using an established model of short-term synaptic plasticity at the single
neuron level, for which we present two different approaches for the derivation
of the mean-field equations. We compare these models with a recently proposed
mean-field approximation that assumes stochastic spike timings. In general, the
latter fails to accurately reproduce the macroscopic activity in networks of
deterministic QIF neurons with distributed parameters. We show that the
mean-field models we propose provide a more accurate description of the network
dynamics, although they are mathematically more involved. Using bifurcation
analysis, we find that QIF networks with pre-synaptic short-term plasticity can
express regimes of periodic bursting activity as well as bi-stable regimes.
Together, we provide novel insight into the macroscopic effects of short-term
synaptic plasticity in spiking neural networks, as well as two different
mean-field descriptions for future investigations of such networks.Comment: 15 pages, 7 figure
Domain Aligned CLIP for Few-shot Classification
Large vision-language representation learning models like CLIP have
demonstrated impressive performance for zero-shot transfer to downstream tasks
while largely benefiting from inter-modal (image-text) alignment via
contrastive objectives. This downstream performance can further be enhanced by
full-scale fine-tuning which is often compute intensive, requires large
labelled data, and can reduce out-of-distribution (OOD) robustness.
Furthermore, sole reliance on inter-modal alignment might overlook the rich
information embedded within each individual modality. In this work, we
introduce a sample-efficient domain adaptation strategy for CLIP, termed Domain
Aligned CLIP (DAC), which improves both intra-modal (image-image) and
inter-modal alignment on target distributions without fine-tuning the main
model. For intra-modal alignment, we introduce a lightweight adapter that is
specifically trained with an intra-modal contrastive objective. To improve
inter-modal alignment, we introduce a simple framework to modulate the
precomputed class text embeddings. The proposed few-shot fine-tuning framework
is computationally efficient, robust to distribution shifts, and does not alter
CLIP's parameters. We study the effectiveness of DAC by benchmarking on 11
widely used image classification tasks with consistent improvements in 16-shot
classification upon strong baselines by about 2.3% and demonstrate competitive
performance on 4 OOD robustness benchmarks.Comment: To appear at WACV 202
The Single-Case Reporting Guideline In BEhavioural Interventions (SCRIBE) 2016 statement
We developed a reporting guideline to provide authors with guidance about what should be reported when writing a paper for publication in a scientific journal using a particular type of research design: the single-case experimental design. This report describes the methods used to develop the Single-Case Reporting guideline In BEhavioural interventions (SCRIBE) 2016. As a result of 2 online surveys and a 2-day meeting of experts, the SCRIBE 2016 checklist was developed, which is a set of 26 items that authors need to address when writing about single-case research. This article complements the more detailed SCRIBE 2016 Explanation and Elaboration article (Tate et al., 2016) that provides a rationale for each of the items and examples of adequate reporting from the literature. Both these resources will assist authors to prepare reports of single-case research with clarity, completeness, accuracy, and transparency. They will also provide journal reviewers and editors with a practical
checklist against which such reports may be critically evaluated. We recommend that the SCRIBE 2016 is used by authors preparing manuscripts describing single-case research for publication, as well as journal reviewers and editors who are evaluating such manuscripts.Funding for the SCRIBE project was provided by the Lifetime Care and Support Authority of New South Wales, Australia. The funding body was not involved in the conduct, interpretation or writing of this work. We acknowledge the contribution of the responders to the Delphi surveys, as well as administrative assistance provided by Kali Godbee and Donna Wakim at the SCRIBE consensus meeting. Lyndsey Nickels was funded by an Australian Research Council Future Fellowship (FT120100102) and Australian Research Council Centre of Excellence in Cognition and Its Disorders (CE110001021). For further discussion on this topic, please visit the Archives of Scientific Psychology online public forum at http://arcblog.apa.org. (Lifetime Care and Support Authority of New South Wales, Australia; FT120100102 - Australian Research Council Future Fellowship; CE110001021 - Australian Research Council Centre of Excellence in Cognition and Its Disorders)Published versio
Interfacial tension and nucleation in mixtures of colloids and long ideal polymer coils
Mixtures of ideal polymers with hard spheres whose diameters are smaller than
the radius of gyration of the polymer, exhibit extensive immiscibility. The
interfacial tension between demixed phases of these mixtures is estimated, as
is the barrier to nucleation. The barrier is found to scale linearly with the
radius of the polymer, causing it to become large for large polymers. Thus for
large polymers nucleation is suppressed and phase separation proceeds via
spinodal decomposition, as it does in polymer blends.Comment: 4 pages (v2 includes discussion of the scaling of the interfacial
tension along the coexistence curve and its relation to the Ginzburg
criterion
Structural Basis for EarP-Mediated Arginine Glycosylation of Translation Elongation Factor EF-P
Glycosylation is a universal strategy to posttranslationally modify proteins. The recently discovered arginine rhamnosylation activates the polyproline-specific bacterial translation elongation factor EF-P. EF-P is rhamnosylated on arginine 32 by the glycosyltransferase EarP. However, the enzymatic mechanism remains elusive. In the present study, we solved the crystal structure of EarP from Pseudomonas putida. The enzyme is composed of two opposing domains with Rossmann folds, thus constituting a B pattern-type glycosyltransferase (GT-B). While dTDP-β-L-rhamnose is located within a highly conserved pocket of the C-domain, EarP recognizes the KOW-like N-domain of EF-P. Based on our data, we propose a structural model for arginine glycosylation by EarP. As EarP is essential for pathogenicity in P. aeruginosa, our study provides the basis for targeted inhibitor design
Flory-Huggins theory for athermal mixtures of hard spheres and larger flexible polymers
A simple analytic theory for mixtures of hard spheres and larger polymers
with excluded volume interactions is developed. The mixture is shown to exhibit
extensive immiscibility. For large polymers with strong excluded volume
interactions, the density of monomers at the critical point for demixing
decreases as one over the square root of the length of the polymer, while the
density of spheres tends to a constant. This is very different to the behaviour
of mixtures of hard spheres and ideal polymers, these mixtures although even
less miscible than those with polymers with excluded volume interactions, have
a much higher polymer density at the critical point of demixing. The theory
applies to the complete range of mixtures of spheres with flexible polymers,
from those with strong excluded volume interactions to ideal polymers.Comment: 9 pages, 4 figure
Phase behaviour of a model of colloidal particles with a fluctuating internal state
Colloidal particles are not simple rigid particles, in general an isolated
particle is a system with many degrees of freedom in its own right, e.g., the
counterions around a charged colloidal particle.The behaviour of model
colloidal particles, with a simple phenomenological model to account for these
degrees of freedom, is studied. It is found that the interaction between the
particles is not pairwise additive. It is even possible that the interaction
between a triplet of particles is attractive while the pair interaction is
repulsive. When this is so the liquid phase is either stable only in a small
region of the phase diagram or absent altogether.Comment: 12 pages including 4 figure
Infection, colonization and shedding of Campylobacter and Salmonella in animals and their contribution to human disease: A review
Livestock meat and offal contribute significantly to human nutrition as sources of high‐quality protein and micronutrients. Livestock products are increasingly in demand, particularly in low‐ and middle‐income settings where economies are growing and meat is increasingly seen as an affordable and desirable food item. Demand is also driving intensification of livestock keeping and processing. An unintended consequence of intensification is increased exposure to zoonotic agents, and a contemporary emerging problem is infection with Campylobacter and Salmonella spp. from livestock (avian and mammalian), which can lead to disease, malabsorption and undernutrition through acute and chronic diarrhoea. This can occur at the farm, in households or through the food chain. Direct infection occurs when handling livestock and through bacteria shed into the environment, on food preparation surfaces or around the house and surroundings. This manuscript critically reviews Campylobacter and Salmonella infections in animals, examines the factors affecting colonization and faecal shedding of bacteria of these two genera as well as risk factors for human acquisition of the infection from infected animals or environment and analyses priority areas for preventive actions with a focus on resource‐poor settings
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