arXiv subjects

Gabriel Dias

Publications and source records attributed to Gabriel Dias.

6 recordsLinked to original sources

arXiv2026

Cell Reproduction in a Dark Optical Trap

Optical tweezers are a versatile tool in the domain of cytology, enabling trapping and manipulation of individual cells. However, the incidence of laser light causes photodamage to biological matter, even when operating at low optical powers and over short periods of time. Here, we demonstrate stable trapping of single living Saccharomyces cerevisiae yeast cells in vitro using a dark optical trap operating in the repulsive regime of light-matter interactions. In contrast to standard tweezers, our dark optical trap confines cells for hours with negligible disruption to their morphology and reproduction cycle, opening up new possibilities for long duration experiments with living organisms such as the observation of cell reproduction under laser trapping.

physics.optics↗

arXiv2026

Heterodyne position detection of an optomechanical system

We report a heterodyne detection scheme for position readout of an optomechanical system, in particular an optically levitated particle, implemented via digital In-phase and Quadrature demodulation on a field-programmable gate array. Compared to the standard homodyne approach, the proposed method offers three key advantages: it remains robust in the presence of strong parasitic back-reflected fields that would otherwise prevent stable phase locking; it produces a signal linearly proportional to the particle displacement, eliminating phase-wrapping distortion; and its calibration factor is intrinsically immune to drifts in the optical power of the local oscillator or scattered field. We experimentally demonstrate and quantify all three advantages through simultaneous homodyne and heterodyne measurements on the same trapped particle. The proposed method can be used in any optomechanical system based on phase readout.

quant-ph↗

arXiv2026

On Meyniel's Conjecture in Random Hypergraphs

The game of \emph{Cops and Robbers} is a two player pursuit game on graphs where a team of cops attempts to catch a robber. The cop number $c(G)$ of a graph $G$ is the minimum number of cops needed to guarantee a winning strategy in $G$. A famous conjecture of Meyniel says that if $G$ is connected, then $c(G)=O(\sqrt{n})$. Erde, Kang, Lehner, Mohar and Schmid considered its generalization to $k$-uniform hypergraphs and conjectured that the cop number of such hypergraphs is $O(\sqrt{n/k})$. This may be understood as a hypergraph version of Meyniel's conjecture. In this paper we prove this conjecture for a class of \textit{expanding} hypergraphs and show that with high probability the conjecture holds for random hypergraphs $H^k(n,p))$ provided $k\geq \log^3n$ and the typical degree, $p\binom{n-1}{k-1}$, is $\omega(\log^3n)$.

math.CO↗

arXiv2025

Signaling in the Age of AI: Evidence from Cover Letters

We study the impact of generative AI on labor market signaling using the introduction of an AI-powered cover letter writing tool on a large online labor platform. Our data track both access to the tool and usage at the application level. Difference-in-differences estimates show that access to the tool increased textual alignment between cover letters and job posts and raised callback rates. Time spent editing AI-generated cover letter drafts is positively correlated with hiring success. After the tool's introduction, the correlation between cover letters' textual alignment and callbacks fell by 51%, consistent with what theory predicts if the AI technology reduces the signal content of cover letters. In response, employers shifted toward alternative signals, including workers' prior work histories.

econ.GN↗

arXiv2024

Moderate Deviations of Triangle Counts in the Erd\H{o}s-R\'enyi Random Graph $G(n,m)$: The Lower Tail

Let $N_{\triangle}(G)$ be the number of triangles in a graph $G$. In [14] and [25] (respectively) the following bounds were proved on the lower tail behaviour of triangle counts in the dense Erd\H{o}s-R\'enyi random graphs $G_m\sim G(n,m)$: \[ \mathbb{P}\big(N_{\triangle}(G_m) \, < \, (1-\delta)\mathbb{E}[N_{\triangle}(G_m)]\big) \,=\, \exp\left(-\Theta\left(\delta^2n^3\right)\right) \qquad \text{if $n^{-3/2}\ll \delta\ll n^{-1}$} \] and \[ \mathbb{P}\big(N_{\triangle}(G_m) \, < \, (1-\delta)\mathbb{E}[N_{\triangle}(G_m)]\big) \,=\, \exp\left(-\Theta(\delta^{2/3}n^2) \right) \qquad \text{if $n^{-3/4} \ll \delta \ll 1$.} \] Neeman, Radin and Sadun [25] also conjectured that the probability should be of the form $\exp\left(-\Theta\left(\delta^2n^3\right)\right)$ in the "missing interval" $n^{-1}\ll \delta\ll n^{-3/4}$. We prove this conjecture. As part of our proof we also prove that some random graph statistics, related to degrees and codegrees, are normally distributed with high probability.

math.CO↗

arXiv2023

Spectro-ViT: A Vision Transformer Model for GABA-edited MRS Reconstruction Using Spectrograms

Purpose: To investigate the use of a Vision Transformer (ViT) to reconstruct/denoise GABA-edited magnetic resonance spectroscopy (MRS) from a quarter of the typically acquired number of transients using spectrograms. Theory and Methods: A quarter of the typically acquired number of transients collected in GABA-edited MRS scans are pre-processed and converted to a spectrogram image representation using the Short-Time Fourier Transform (STFT). The image representation of the data allows the adaptation of a pre-trained ViT for reconstructing GABA-edited MRS spectra (Spectro-ViT). The Spectro-ViT is fine-tuned and then tested using \textit{in vivo} GABA-edited MRS data. The Spectro-ViT performance is compared against other models in the literature using spectral quality metrics and estimated metabolite concentration values. Results: The Spectro-ViT model significantly outperformed all other models in four out of five quantitative metrics (mean squared error, shape score, GABA+/water fit error, and full width at half maximum). The metabolite concentrations estimated (GABA+/water, GABA+/Cr, and Glx/water) were consistent with the metabolite concentrations estimated using typical GABA-edited MRS scans reconstructed with the full amount of typically collected transients. Conclusion: The proposed Spectro-ViT model achieved state-of-the-art results in reconstructing GABA-edited MRS, and the results indicate these scans could be up to four times faster.

eess.IV↗