arXiv subjects

David Rodriguez

Publications and source records attributed to David Rodriguez.

At least 19 recordsLinked to original sources

arXiv2026

Evidence for superconductivity at 190 K in a pressure-overdoped cuprate

It is well established that the critical temperature ($T_c$) of cuprate superconductors can be tuned by pressure. For example, compression decouples the hole doping from chemical doping allowing for overdoped samples far beyond what is possible at ambient pressure. In this work, multiple techniques are used to probe the onset of the Meissner effect at $T_c$ as a function of pressure in $\mathrm{Pb_{0.4}Bi_{1.6}Sr_2Ca_2Cu_3O_{10+\delta}}$ (Bi-2223) to 60 GPa in different compression environments. Samples compressed under quasihydrostatic conditions exhibit a distinctive non-monotonic pressure dependence of $T_c$ below 25 GPa, in agreement with previous reports. With further increase in pressure $T_c$ climbs continuously to 190 K at 60 GPa. Evidence for critical temperatures exceeding those reported to date for cuprates at ambient and high pressures, the results may be understood in terms of the proposed second superconducting regime at high hole doping.

cond-mat.supr-con↗

arXiv2026

Enabling Multilingual Privacy Policy Audits: Large-Scale Analysis of Spanish Mobile Apps

Automated analyses of privacy policies enable large-scale assessments of transparency in digital ecosystems, yet existing auditing pipelines remain predominantly English-centric. This limits their ability to systematically evaluate multilingual environments, as in the European Union, where many services disclose privacy practices only in local languages. This paper examines whether large language models (LLMs) can extend privacy policy analysis beyond English without requiring language-specific adaptation, thus empowering large-scale auditing in linguistically diverse app ecosystems. We assemble an evaluation corpus spanning all 24 official EU languages from translated versions of two established expert-annotated datasets (OPP-115 and MAPP) and assess translation fidelity through automated metrics and targeted legal-expert review. Our LLM-based classifier for identifying categories of personal data collection achieves stable cross-lingual performance, with macro-F1 scores ranging between 0.91 and 0.94. We then leverage this capability in a large-scale audit of 2,611 Android applications from the Spanish Google Play Store. Combining multilingual privacy policy analysis with the evaluation of corresponding privacy labels and runtime network traffic exposes an important linguistic barrier: public-sector apps predominantly provide privacy policies in Spanish, whereas popular commercial apps mostly provide them in English. We reveal systematic discrepancies between declared and observed practices, especially in public-sector apps. Overall, our results indicate how English-only privacy audits can systematically obfuscate transparency gaps in multilingual environments.

cs.CY↗

arXiv2026

Do Generative AI Assistants Respect robots.txt? Tracing Web Access Beyond Visible Answers

AI assistants increasingly retrieve web content at inference time to provide fresh and grounded answers, yet it remains unclear whether these search-augmented capabilities respect website-owner restrictions expressed through robots$.$txt. We present a controlled empirical study of ten widely used AI assistants with advertised web-search capabilities. For each assistant, we first identify a configuration that actually produces observable web-browsing behavior and record the user-agent exposed during retrieval. We then evaluate compliance with controlled robots$.$txt rules across four complementary conditions: allowed for all user-agents, disallowed for all user-agents, allowed only for the assistant-specific user-agent, and disallowed only for that user-agent. Using server-side logs and secret codes embedded in target pages, we distinguish actual page access from user-visible answer correctness across 200 trials. Our results show substantial variation across assistants. Some systems followed the expected allowed/disallowed access pattern, whereas others accessed restricted resources without requesting robots$.$txt or used generic user-agents that complicated attribution. We also find that retrieval behavior and answer correctness can diverge: assistants may access pages without surfacing the retrieved content, or fail to access even allowed resources. These findings raise broader legal and governance concerns about whether AI-assisted web access adequately respects content owners' rights and restrictions. Furthermore, our observations provide valuable insight into the growing erosion of traditional web governance protocols, highlighting the urgent need for updated, enforceable standards that guarantee publisher autonomy in the age of search-augmented AI assistants.

cs.CY↗

arXiv2026

The Hubble Advanced Spectral Product (HASP) Program

The Hubble Advanced Spectral Products (HASP) program is designed to robustly coadd Cosmic Origins Spectrograph (COS) and Space Telescope Imaging Spectrograph (STIS) spectra within the Mikulski Archive for Space Telescopes (MAST) in an automated fashion such that coadds are available for new data or archival data with updated calibrations. For each target within a visit or program, HASP employs a meticulous multi-stage filtering process to ensure data quality and creates coadded products for all central wavelengths (CENWAVEs) within specific gratings, as well as combined products using different gratings and instruments. The project also emphasizes making the code accessible to the user community for custom coaddition. As calibrations improve and new data are added to the archive, HASP products are re-created automatically so that they represent the best reduction of a given visit or program. Automated coadditions like those achieved by HASP can significantly enhance the combination of different CENWAVES, increase signal-to-noise ratios, and increase wavelength coverage. These properties make HASP a vital resource for astronomers using archival spectroscopic data from HST.

astro-ph.IM↗

arXiv2026

Overview of the New Hubble Spectroscopic Legacy Archive

The new Hubble Spectroscopic Legacy Archive (HSLA) provides coadded spectra of individual targets that have been observed with the Cosmic Origins Spectrograph (COS) and the Space Telescope Imaging Spectrograph (STIS) over their operating lifetime. HSLA uses data available in the Mikulski Archive for Space Telescopes (MAST). It automatically produces coadds whenever new data become publicly available or when there is newly recalibrated data. HSLA defines individual targets by their associated coordinates, accounting for proper motions, and uses SIMBAD, NED and the Phase II observing proposals to obtain astronomical classifications for each object. Coadded spectra are produced for each observing mode. In the case of COS far-ultraviolet observations there is one coadded spectrum for each lifetime position (LP). Additionally, a spectrum spanning the entire wavelength range covered by the observations is produced by abutting the spectra from a selection of individual modes. For each individual target, HSLA also provides a human-readable metadata file with key information that can be used in searches or for further exploration of the data. The HSLA project also makes the code used for coadding spectra publicly available along with several other tools (using Jupyter notebooks) for custom coaddition required in special cases. In this report we will describe the main components of HSLA and provide a brief description of how the data and metadata can be accessed.

astro-ph.IM↗

arXiv2026

Polariton-polariton coherent coupling in a molecular spin-superconductor chip

The ability to establish coherent communication channels is key for scaling up quantum devices. Here, we engineer interactions between distant polaritons, hybrid spin-photon excitations formed at different lumped-element superconducting resonators within a chip. The chip consists of several resonator pairs, slightly detuned in frequency to make them addressable, capacitively coupled within each pair and inductively coupled to a common readout line. They interact locally with samples of PTMr and Tripak$^{-}$ organic free radicals, deposited onto their inductors, which provide model $S = 1/2$, $g \simeq 2$ spin ensembles. Frequency-dependent microwave transmission experiments, performed at very low temperatures, measure polariton frequencies as a function of magnetic field in different scenarios. When only one resonator within a pair hosts a molecular sample, the results evidence that spins couple remotely to the empty LER as well as to the local cavity mode. If both resonators interact with a spin ensemble, the magnetic field tunes the polariton frequencies relative to each other, on account of the different spin-photon interactions at each LER. When polaritons are brought into mutual resonance, an avoided level crossing emerges that gives direct spectroscopic evidence for a coherent polariton-polariton interaction mediated by the circuit. Pump-probe experiments reveal that the excitation of a polariton within a connected pair is felt, thus it can be read out, by the other one. These observations, backed by model calculations, illustrate the control and detection of distant photon-photon and spin-spin correlations and entanglement in a scalable modular chip.

quant-ph↗

arXiv2026

Two warm sub-Saturn mass planets identified from the TESS Full Frame Images

Context. Characterization of warm giants is crucial to constrain giant planet formation and evolution. Measuring the mass and radius of these planets, combined with their moderated irradiation, allows us to estimate their planetary bulk composition, which is a key quantity to comprehend giant planet formation and structure. Aims. We present the discovery of two transiting warm giant planets orbiting solar-type stars from the Transiting Exoplanet Survey Satellite (TESS), which were characterized by further spectroscopic and photometric ground-based observations. Methods. We performed a joint analysis of photometric data with radial velocities to confirm and characterize TOI-883 b and TOI-899 b, two sub-Saturns orbiting solar-like stars. Results. TOI-883 b and TOI-899 b have masses of $0.123 \pm 0.012$ $M_J$ and $0.213 \pm 0.024$ $M_J$, radius of $0.604 \pm 0.028$ $R_J$ and $0.991 \pm 0.044$ $R_J$, periods of $10.06$ d and $12.85$ d and equilibrium temperature of $1086 \pm 19$ K and $1040 \pm 19$ K, respectively. Conclusions. While having similar masses, orbital periods and stellar host properties, these planets seem to have different internal compositions, which could point to distinct formation histories. Both planets are suitable targets for atmospheric studies to further constrain formation scenarios of planets in the Neptune-Saturn mass range

astro-ph.EP↗

arXiv2025

Optimizing magnetic coupling in lumped element superconducting resonators for molecular spin qubits

We engineer lumped-element superconducting resonators that maximize magnetic coupling to molecular spin qubits, achieving record single-spin couplings up to $100$ kHz and collective couplings exceeding $10$ MHz. The resonators interact with PTMr organic free radicals, model spin systems with $S=1/2$ and a quasi-isotropic $g \simeq 2$, dispersed in polymer matrices. The highest collective spin-photon coupling strengths are attained with resonators having large inductors, which therefore interact with most spins in the molecular ensemble. By contrast, the coupling of each individual spin $G_{1}$ is maximized in resonators having a minimum size inductor, made of a single wire. The same platform has been used to study spin relaxation and spin coherent dynamics in the dispersive regime, when spins are energetically detuned from the resonator. We find evidences for the Purcell effect, i.e. the photon induced relaxation of those spins that are most strongly coupled to the circuit. The rate of this process gives access to the distribution of single spin photon couplings in a given device. For resonators with a $50$ nm wide constriction at the inductor center, single maximum $G_{1}$ values reach $\sim 100$ kHz. Pumping the spins with strong pulses fed through an independent transmission line induces coherent Rabi oscillations. The spin excitation then proceeds via either direct resonant processes induced by the main pulse frequency or, in the case of square-shaped pulses, via the excitation of the cavity by sideband frequency components. The latter process measures the cavity mode hybridization with the spins and can be eliminated by using Gaussian shaped pulses. These results establish a scalable route toward integrated molecular-spin quantum processors.

quant-ph↗

arXiv2025

Overcoming Language Barriers: Multilingual Analysis of the 2023 Swiss Privacy Law's Impact

Policymakers enact and revise privacy laws expecting meaningful benefits for their people in practice. While scholarship has measured the real-world impact of some privacy regulations-the EU and California most notably-limited empirical evidence exists for many of the more than 140 countries that have implemented some form of privacy legislation. Switzerland, a multilingual country bordered almost entirely by EU states, is one such example. This paper analyzes the extent to which a 2023 alignment of Swiss privacy law with EU privacy regulation affected website privacy policies in Switzerland. To address Switzerland's unique multilingual culture, we develop an LLM-based pipeline that extracts legally relevant information as document-level labels in a single inference without requiring translation. On a benchmark of 120 expert-annotated privacy policies in German, French, Italian, and English, our pipeline achieves F1 scores above 0.90 for most pairs of languages and legally relevant disclosures. Applying this pipeline to privacy policies we collected from more than 35,000 Swiss- and EU-facing websites before and after the 2023 privacy law revision, we find significant increases in both mandatory and voluntary disclosures of data subject rights among Swiss privacy policies. In exploring the mechanisms driving increased disclosure rates, we discover heavy use of automated privacy policy generators and find that generated policies are associated with up to 15 percentage points higher disclosure rates. These results provide large-scale empirical evidence of how regulatory change and novel drafting technologies impact the content of privacy policies in a unique multilingual environment.

cs.CL↗

arXiv2025

Millimeter-Wavelength Lens-Absorber-Coupled Ti/Al Kinetic Inductance Detectors

This work presents Ti/Al bi-layer Microwave Kinetic Inductance Detectors (MKIDs) based on lens-coupled spiral absorbers as the quasi-optical coupling mechanism for millimeter-wavelength radiation detection. From simulations, the lens-coupled absorbers provide a 70% lens aperture efficiency in both polarizations over an octave band with a spiral array absorber and over 10% relative bandwidth with a single spiral. We have fabricated and measured two devices with bare Ti/Al MKIDs: a 3x3 cm chip with 9 pixels to characterize the optical response at 85 GHz of the two variations of the absorber; and a large format demonstrator with 253 spiral-array pixels showing potential towards a large format millimeter-wavelength camera. We estimate a sensitivity of 1 $\mathrm{mK}\cdot\mathrm{Hz}^{-0.5}$ and a 95% detector yield.

astro-ph.IM↗

arXiv2025

Cross-Polarization Reduction in Kinetic Inductance Detectors Based on Quasi-Lumped Resonators

Kinetic Inductance Detectors (KIDs) have emerged as a leading technology for millimeter- and submillimeter-wave astronomy due to their high sensitivity, natural multiplexing capabilities and scalable fabrication. In polarization-sensitive applications-such as Cosmic Microwave Background (CMB) studies-cross-polarization, or unintended response to the orthogonal polarization, poses a significant limitation to measurement fidelity. This work investigates the origin of cross-polarization in meandered Lumped Element KIDs (LEKIDs), with particular emphasis on the role of parasitic currents in the interdigitated capacitor. A comparative study between conventional LEKIDs and a quasi-lumped resonator design is presented, demonstrating that removing the capacitive element may improve cross-polarization discrimination, confirming the capacitor's contribution to polarization leakage.

astro-ph.IM↗

arXiv2025

Dark characterization of Ti/Al LEKIDs for the search of axions in the W-band

We report the electrical (dark) characterization of lumped-element kinetic inductance detectors (LEKIDs) fabricated from a Titanium/Aluminum bilayer and designed for broadband absorption in the W-band (75-110 GHz). These detectors are prototypes for future QCD axion search experiments within the Canfranc Axion Detection Experiment (CADEx), which demand sub 1e-19 W/Hz^0.5 sensitivities under low optical backgrounds. We combine a Mattis-Bardeen analysis to the temperature dependence of the detector parameters with noise spectroscopy to determine the electrical noise equivalent power (NEP). The minimum measured value for the electrical NEP is 3e-19 W/Hz0.5. Across the measured temperature range, we find that quasiparticle lifetime deviates from the expected BCS recombination law. Our analysis suggests that non-equilibrium relaxation is governed by spatial inhomogeneities in the superconducting gap and phonon diffusion effects. This work sets the road-map to achieve suitable and ultra-sensitive detectors in the W-band for dark matter axion search experiments.

physics.ins-det↗

arXiv2025

Towards Safer Chatbots: Automated Policy Compliance Evaluation of Custom GPTs

User-configured chatbots built on top of large language models are increasingly available through centralized marketplaces such as OpenAI's GPT Store. While these platforms enforce usage policies intended to prevent harmful or inappropriate behavior, the scale and opacity of customized chatbots make systematic policy enforcement challenging. As a result, policy-violating chatbots continue to remain publicly accessible despite existing review processes. This paper presents a fully automated method for evaluating the compliance of Custom GPTs with its marketplace usage policy using black-box interaction. The method combines large-scale GPT discovery, policy-driven red-teaming prompts, and automated compliance assessment using an LLM-as-a-judge. We focus on three policy-relevant domains explicitly addressed in OpenAI's usage policies: Romantic, Cybersecurity, and Academic GPTs. We validate our compliance assessment component against a human-annotated ground-truth dataset, achieving an F1 score of 0.975 for binary policy violation detection. We then apply the method in a large-scale empirical study of 782 Custom GPTs retrieved from the GPT Store. The results show that 58.7% of the evaluated GPTs exhibit at least one policy-violating response, with substantial variation across policy domains. A comparison with the base models (GPT-4 and GPT-4o) indicates that most violations originate from model-level behavior, while customization tends to amplify these tendencies rather than create new failure modes. Our findings reveal limitations in current review mechanisms for user-configured chatbots and demonstrate the feasibility of scalable, behavior-based policy compliance evaluation.

cs.CL↗

arXiv2024

Spectroscopic Observations of the Galex Nearby Young Star Survey Sample. 1. Nearby Moving Group Candidates

The GALEX Nearby Young Star Search (GALNYSS) yielded the identification of more than 2000 late-type stars that, based on their ultraviolet and infrared colors and pre-Gaia proper motions, are potentially of age < 200 Myr and lie within ~120 pc of Earth. We present the results of a campaign of medium- and high-resolution optical spectroscopy of 471 GALNYSS stars aimed at confirming their youth and their potential membership in nearby young stellar moving groups. We present radial velocity (RV), Li absorption, and H-$\alpha$ emission measurements for these spectroscopically observed GALNYSS stars, and assess their Li absorption and optical emission-line properties and infrared excesses. Our RV measurements are combined with literature and Gaia DR3 RV measurements and Gaia DR3 astrometry and photometry to obtain the spatiokinematics and color-magnitude positions of GALNYSS stars. We use these results to assess membership in the TW Hya, Tuc-Hor, Carina, Columba, and Argus Associations and the $\beta$-PMG and AB Dor moving groups. We have identified 132 stars as candidate members of these seven groups; roughly half of these candidates are newly identified on the basis of data presented here. At least one-third of the 132 candidates are spectroscopic and/or photometric binaries and/or have comoving (visual) binary companions in Gaia DR3. The contingent of young, low-mass stars in the solar vicinity we identify here should provide excellent subjects for future direct imaging exoplanet surveys and studies of the early evolution of low-mass stars and their planetary progeny.

astro-ph.SR↗

arXiv2024

Large Language Models: A New Approach for Privacy Policy Analysis at Scale

The number and dynamic nature of web and mobile applications presents significant challenges for assessing their compliance with data protection laws. In this context, symbolic and statistical Natural Language Processing (NLP) techniques have been employed for the automated analysis of these systems' privacy policies. However, these techniques typically require labor-intensive and potentially error-prone manually annotated datasets for training and validation. This research proposes the application of Large Language Models (LLMs) as an alternative for effectively and efficiently extracting privacy practices from privacy policies at scale. Particularly, we leverage well-known LLMs such as ChatGPT and Llama 2, and offer guidance on the optimal design of prompts, parameters, and models, incorporating advanced strategies such as few-shot learning. We further illustrate its capability to detect detailed and varied privacy practices accurately. Using several renowned datasets in the domain as a benchmark, our evaluation validates its exceptional performance, achieving an F1 score exceeding 93%. Besides, it does so with reduced costs, faster processing times, and fewer technical knowledge requirements. Consequently, we advocate for LLM-based solutions as a sound alternative to traditional NLP techniques for the automated analysis of privacy policies at scale.

cs.CL↗

arXiv2024

Low loss hybrid Nb/Au superconducting resonators for quantum circuit applications

Superconducting resonators play a crucial role in the development of quantum technologies such as quantum computing or high performance detectors. Yet, one of their main limitations regarding to noise and sensitivity is the interaction with two-level systems present in oxide layers in the device. Focused on mitigating this problem, we study a superconducting device combining a 100 nm niobium (Nb) circuit with a 10 nm gold (Au) capping layer. Our investigation covers a wide range of temperatures and driving powers, revealing that adding the Au layer reduces the density of two-level system defects while maintaining a very high quality factor. Moreover, an increase in the non-linearity response is also observed. Our findings suggest the potential of Nb/Au lumped element resonators as versatile and promising tools for advancing superconducting quantum technologies.

quant-ph↗

arXiv2024

Biofilm growth on rugose surfaces

A stochastic model is used to assess the effect of external parameters on the development of submerged biofilms on smooth and rough surfaces. The model includes basic cellular mechanisms, such as division and spreading, together with an elementary description of the interaction with the surrounding flow and probabilistic rules for EPS matrix generation, cell decay and adhesion. Insight on the interplay of competing mechanisms as the flow or the nutrient concentration change is gained. Erosion and growth processes combined produce biofilm structures moving downstream. A rich variety of patterns are generated: shrinking biofilms, patches, ripple-like structures traveling downstream, fingers, mounds, streamer-like patterns, flat layers, porous and dendritic structures. The observed regimes depend on the carbon source and the type of bacteria.

cond-mat.soft↗

arXiv2023

Discovery and characterisation of two Neptune-mass planets orbiting HD 212729 with TESS

We report the discovery of two exoplanets orbiting around HD 212729 (TOI\,1052, TIC 317060587), a $T_{\rm eff}=6146$K star with V=9.51 observed by TESS in Sectors 1 and 13. One exoplanet, TOI-1052b, is Neptune-mass and transits the star, and an additional planet TOI-1052c is observed in radial velocities but not seen to transit. We confirm the planetary nature of TOI-1052b using precise radial velocity observations from HARPS and determined its parameters in a joint RV and photometry analysis. TOI-1052b has a radius of $2.87^{+0.29}_{-0.24}$ R$_{\oplus}$, a mass of $16.9\pm 1.7$ M$_{\oplus}$, and an orbital period of 9.14 days. TOI-1052c does not show any transits in the TESS data, and has a minimum mass of $34.3^{+4.1}_{-3.7}$ M$_{\oplus}$ and an orbital period of 35.8 days, placing it just interior to the 4:1 mean motion resonance. Both planets are best fit by relatively high but only marginally significant eccentricities of $0.18^{+0.09}_{-0.07}$ for planet b and $0.24^{+0.09}_{-0.08}$ for planet c. We perform a dynamical analysis and internal structure model of the planets as well as deriving stellar parameters and chemical abundances. The mean density of TOI-1052b is $3.9^{+1.7}_{-1.3}$ g cm$^{-3}$ consistent with an internal structure similar to Neptune. A nearby star is observed in Gaia DR3 with the same distance and proper motion as TOI-1052, at a sky projected separation of ~1500AU, making this a potential wide binary star system.

astro-ph.EP↗