IST Austria: PubRep (Institute of Science and Technology)
Not a member yet
6140 research outputs found
Sort by
ISTA Thesis
No full textMaking decisions requires flexibly adapting to changing environments, a process that
depends on accurately interpreting current contingencies and integrating them with
past experience. Two brain regions are particularly critical for this process, the medial
prefrontal cortex (mPFC) and the hippocampus. Using contextual information from the
hippocampus, the mPFC selects relevant cognitive frameworks and suppresses
irrelevant ones to guide appropriate actions. Several studies have shown that some
mPFC pyramidal neurons become spatially tuned when spatial information is required
to guide goal-directed behavior. However, the role of prefrontal spatial representations
in learning and decision making is not well understood. This work aims to characterize
the role of mPFC spatial tuning in supporting a contextual association task. Rats were
trained to learn two cue–location associations on a radial arm maze over multiple days,
while we simultaneously recorded from dorsal CA1 of the hippocampus and the
prelimbic area of the mPFC. We describe a subset of spatially tuned hippocampal and
prefrontal pyramidal neurons that “flicker” between multiple spatial representations on
different trials, suggesting dynamic, context-dependent coding. This flickering may
provide a substrate for how the network reorganizes in response to task demands,
likely by enabling the flexible evaluation of competing representations
Extremal, enumerative and probabilistic results on ordered hypergraph matchings
No full textAn ordered r-matching is an r-uniform hypergraph matching equipped with an ordering on its vertices. These objects can be viewed as natural generalisations of r-dimensional orders. The theory of ordered 2-matchings is well developed and has connections and applications to extremal and enumerative combinatorics, probability and geometry. On the other hand, in the case r≥3 much less is known, largely due to a lack of powerful bijective tools. Recently, Dudek, Grytczuk and Ruciński made some first steps towards a general theory of ordered r-matchings, and in this paper we substantially improve several of their results and introduce some new directions of study. Many intriguing open questions remain
Intriguing properties of robust classification
No full textDespite extensive research since the community learned about adversarial examples 10 years ago, we still do not know how to train high-accuracy classifiers that are guaranteed to be robust to small perturbations of their inputs. Previous works often argued that this might be because no classifier exists that is robust and accurate at the same time. However, in computer vision this assumption does not match reality where humans are usually accurate and robust on most tasks of interest. We offer an alternative explanation and show that in certain settings robust generalization is only possible with unrealistically large amounts of data. Specifically, we find a setting where a robust classifier exists, it is easy to learn an accurate classifier, yet it requires an exponential amount of data to learn a robust classifier. Based on this theoretical result, we evaluate the influence of the amount of training data on datasets such as CIFAR10. Our findings indicate that the the amount of training data is the main factor determining the robust performance. Furthermore we show that that there are low magnitude directions in the data which are useful for non-robust generalization but are not available for robust classifiers. This implies that robust classification is a strictly harder tasks than normal classification, thereby providing an explanation why robust classification requires more data
Exploring how to authenticate application messages in MLS: More efficient, post-quantum, and anonymous blocklistable
No full textThe Message Layer Security (MLS) protocol has recently been standardized by the IETF. MLS is a scalable secure group messaging protocol expected to run more efficiently compared to the Signal protocol at scale, while offering a similar level of strong security. Even though MLS has undergone extensive examination by researchers, the majority of the works have focused on confidentiality.
In this work, we focus on the authenticity of the application messages exchanged in MLS. Currently, MLS authenticates every application message with an EdDSA signature and while manageable, the overhead is greatly amplified in the post-quantum setting as the NIST-recommended Dilithium signature results in a 40x increase in size. We view this as an invitation to explore new authentication modes that can be used instead. We start by taking a systematic view on how application messages are authenticated in MLS and categorize authenticity into four different security notions. We then propose several authentication modes, offering a range of different efficiency and security profiles. For instance, in one of our modes, COSMOS++, we replace signatures with one-time tokens and a MAC tag, offering roughly a 75x savings in the post-quantum communication overhead. While this comes at the cost of weakening security compared to the authentication mode used by MLS, the lower communication overhead seems to make it a worthwhile trade-off with security
Mechanical control of cell fate decisions in the skin epidermis
No full textHomeostasis relies on a precise balance of fate choices between renewal and differentiation. Although progress has been done to characterize the dynamics of single-cell fate choices, their underlying mechanistic basis often remains unclear. Concentrating on skin epidermis as a paradigm for multilayered tissues with complex fate choices, we develop a 3D vertex-based model with proliferation in the basal layer, showing that mechanical competition for space naturally gives rise to homeostasis and neutral drift dynamics that are seen experimentally. We then explore the effect of introducing mechanical heterogeneities between cellular subpopulations. We uncover that relatively small tension heterogeneities, reflected by distinct morphological changes in single-cell shapes, can be sufficient to heavily tilt cellular dynamics towards exponential growth. We thus derive a master relationship between cell shape and long-term clonal dynamics, which we validated during basal cell carcinoma initiation in mouse epidermis. Altogether, we propose a theoretical framework to link mechanical forces, quantitative cellular morphologies and cellular fate outcomes in complex tissues
Deep eutectic solvent as a solution for polyester/cotton textile recycling
No full textGlobal fibre production has expanded rapidly, with polyester and cotton dominating, significantly contributing to textile waste and increasing demand for sustainable solutions. This study presents innovative method to recycle polyester/cotton (PET/CO) blends using hydrophobic deep eutectic solvents (DESs), eliminating the need for toxic chemicals while achieving high dissolution yields. PET was completely dissolved within 5 min, substantially outperforming state-of-the-art methods and facilitating the efficient and selective recovery of both components, PET (97%) and CO (100%). SEM imaging confirmed no morphological changes in cotton fibres after treatment. The thermal stability of the recovered materials was validated using DSC and TGA analyses, while ATR-FTIR spectroscopy indicated no chemical changes. Mechanical testing confirmed recovered cotton’s tenacity and elongation are within expected ranges despite showing a decrease of 28% in tenacity and 34% in elongation. Hence, the proposed process provides an efficient and sustainable recycling solution for PET/CO blends, retaining both polymers in a condition similar to virgin materials used in textile manufacturing with minimal processing time
Radiative corrections to the dynamics of a tracer particle coupled to a Bose ccalar field
No full textWe consider a tracer particle coupled to a Bose scalar field and study the regime where the field’s propagation speed approaches infinity. For initial states devoid of field excitations, we introduce an effective approximation of the time-evolved wave function and prove its validity in Hilbert space norm. In this approximation, the field remains in the vacuum state, while the tracer particle propagates with a modified dispersion relation. Physically, the new dispersion relation can be understood as the effect of radiative corrections due to interactions with virtual bosons. Mathematically, it is defined as the solution of a self-consistent nonlinear equation, whose form depends on the relevant time scale
Poisson-Nernst-Planck charging dynamics of an electric double-layer capacitor: Symmetric and asymmetric binary electrolytes
No full textA parallel plate capacitor containing an electrolytic solution is the simplest model of a supercapacitor or electric double-layer capacitor. Using both analytical and numerical techniques, we solve the Poisson-Nernst-Planck equations for such a system, describing the mean-field charging dynamics of the capacitor, when a constant potential difference is abruptly applied to its plates. Working at constant total number of ions, we focus on the physical processes involved in the relaxation and, whenever possible, give its functional shape and exact time constants. We first review and study the case of a symmetric binary electrolyte, where we assume the two ionic species to have the same charges and diffusivities. We then relax these assumptions and present results for a generic strong (i.e fully dissociated) binary electrolyte. At low electrolyte concentration, the relaxation is simple to understand, as the dynamics of positive and negative ions appear decoupled. At higher electrolyte concentration, we distinguish several regimes. In the linear regime (low voltages), relaxation is multiexponential, it starts by the buildup of the equilibrium charge profile and continues with neutral mass diffusion, and the relevant timescales feature both the average and the Nernst-Hartley diffusion coefficients. In the purely nonlinear regime (intermediate voltages), the initial relaxation is slowed down exponentially due to increased capacitance, while bulk effects become more and more evident. In the fully nonlinear regime (high voltages), the dynamics of charge and mass are completely entangled and, asymptotically, the relaxation is linear in time. We finally discuss nonideal behavior in real capacitors and provide conditions for which mean-field is expected to hold
RUBIES: A spectroscopic census of little red dots
No full textThe physical nature of little red dots (LRDs), a population of compact red galaxies revealed by JWST, remains unclear. Photometric samples were constructed from varying selection criteria with limited spectroscopic follow-up available to test intrinsic spectral shapes and the prevalence of broad emission lines. We used the RUBIES survey, a large spectroscopic program with wide color-morphology coverage and homogeneous data quality, to systematically analyze the emission-line kinematics, spectral shapes, and morphologies of ∼1500 galaxies at z > 3.1. We identified broad Balmer lines via a novel fitting approach that simultaneously models NIRSpec/PRISM and G395M spectra, yielding 80 broad-line sources with 28 (35%) at z > 6. A large subpopulation naturally emerged from the broad Balmer line sources, with 36 exhibiting v-shaped UV-to-optical continua and a dominant point source component in the rest-optical; we define these as spectroscopic LRDs, constituting the largest such sample to date. Strikingly, the spectroscopic LRD population is largely recovered when either a broad line or rest-optical point source is required in combination with a v-shaped continuum, suggesting an inherent link between these three defining characteristics. We compared the spectroscopic LRD sample to published photometric searches. Although these selections have high accuracy, 80%−95% down to F444W < 26.5, only 50%−80% of the RUBIES LRDs were photometrically identified, depending on the selection criteria used. The remainder were missed due to a mixture of faint rest-UV photometry, comparatively blue rest-optical colors, or highly uncertain photometric redshifts. Our findings highlight that well-selected spectroscopic campaigns are essential for robust LRD identification, while photometric criteria require refinement to capture the full population
The first direct imaging of the silhouette of a damped Lyman α system along the line-of-sight to a background galaxy
No full textThe H i gas distribution in damped Lyman absorbers (DLAs) has remained elusive due to the point-source nature of background quasar emission. Observing DLAs against spatially extended background galaxies provides a new method for constraining their size and structure. Using the Keck Cosmic Web Imager, we present the first ‘silhouette’ image of a DLA at , identified in the spectrum of a background galaxy at . Although the silhouette remains unresolved due to limited spatial resolution, this represents a successful proof-of-concept for studying DLA morphology using extended background sources. Possible residual emission in the DLA trough suggests an optical depth contrast exceeding in the internal structure, implying a sharp edge or patchy structure. A Lyman emitter (LAE) at , consistent with the DLA redshift, is detected at an angular separation of ( kpc). The DLA is surrounded by three galaxies within 140 kpc in projected distance and 500 km s in line-of-sight velocity, indicating that it resides in the circumgalactic medium of the LAE or within a galaxy group/protocluster environment. An O i absorption at is also detected along the line of sight. This absorber may trace metal-enriched outflow from the LAE or a gas-rich galaxy exhibiting the highest star formation activity among the surrounding galaxies. Future large spectroscopic surveys of galaxies will expand such a DLA sample, and three-dimensional spectroscopy for it will shed new light on the role of intergalactic dense gas in galaxy formation and evolution