arXiv subjects

Joshua Davis

Publications and source records attributed to Joshua Davis.

7 recordsLinked to original sources

arXiv2026

Symmetry-Engineered Magnetic Dipole Emission in Plasmonic Core-Satellite Resonators

Magnetic dipole (MD) transitions are intrinsically weak and highly sensitive to emitter orientation and position, making their controlled enhancement at optical frequencies particularly challenging. Here we show that structural symmetry provides a powerful route to robust magnetic light-matter interactions. We systematically investigate plasmonic core-satellite resonators composed of N metallic nanoparticles arranged on a dielectric core. We evaluate their performance using a unified figure of merit that accounts for magnetic Purcell enhancement, electric dipole suppression, quantum efficiency, and robustness to emitter orientation and fabrication tolerances. We find that the optimal structures correspond to the highest-symmetry geometries, which naturally produce spatially homogeneous and orientation-independent magnetic Purcell enhancement. In particular, the dodecapod configuration yields strong magnetic emission with Purcell factors approaching 250, high radiative efficiency, and suppressed electric dipole contributions. Quasinormal-mode and complex mode-volume analysis reveal that symmetry enforces uniform magnetic modal confinement within the core, explaining both the enhancement and its robustness. These results establish symmetry as a guiding principle for designing nanophotonic resonators with controlled multipolar light-matter interactions and provide a practical route toward bright and selective magnetic dipole emitters.

physics.optics↗

arXiv2025

BioClinical ModernBERT: A State-of-the-Art Long-Context Encoder for Biomedical and Clinical NLP

Encoder-based transformer models are central to biomedical and clinical Natural Language Processing (NLP), as their bidirectional self-attention makes them well-suited for efficiently extracting structured information from unstructured text through discriminative tasks. However, encoders have seen slower development compared to decoder models, leading to limited domain adaptation in biomedical and clinical settings. We introduce BioClinical ModernBERT, a domain-adapted encoder that builds on the recent ModernBERT release, incorporating long-context processing and substantial improvements in speed and performance for biomedical and clinical NLP. BioClinical ModernBERT is developed through continued pretraining on the largest biomedical and clinical corpus to date, with over 53.5 billion tokens, and addresses a key limitation of prior clinical encoders by leveraging 20 datasets from diverse institutions, domains, and geographic regions, rather than relying on data from a single source. It outperforms existing biomedical and clinical encoders on four downstream tasks spanning a broad range of use cases. We release both base (150M parameters) and large (396M parameters) versions of BioClinical ModernBERT, along with training checkpoints to support further research.

cs.CL↗

arXiv2025

MedSlice: Fine-Tuned Large Language Models for Secure Clinical Note Sectioning

Extracting sections from clinical notes is crucial for downstream analysis but is challenging due to variability in formatting and labor-intensive nature of manual sectioning. While proprietary large language models (LLMs) have shown promise, privacy concerns limit their accessibility. This study develops a pipeline for automated note sectioning using open-source LLMs, focusing on three sections: History of Present Illness, Interval History, and Assessment and Plan. We fine-tuned three open-source LLMs to extract sections using a curated dataset of 487 progress notes, comparing results relative to proprietary models (GPT-4o, GPT-4o mini). Internal and external validity were assessed via precision, recall and F1 score. Fine-tuned Llama 3.1 8B outperformed GPT-4o (F1=0.92). On the external validity test set, performance remained high (F1= 0.85). Fine-tuned open-source LLMs can surpass proprietary models in clinical note sectioning, offering advantages in cost, performance, and accessibility.

cs.CL↗

arXiv2014

A Covert Channel Based on Web Read-time Modulation

A network covert channel is created that operates by modulating the time between web resource accesses, with an 'average web user' read-time used as a reference. While the covert channel may be classified as timing based, it does not operate by changing deterministic protocol attributes such as inter-packet delay, as do most timing based network covert channels. Instead, our channel communicates by modulating transaction level read-time, which in the web browsing case has significant non-deterministic components. The channel is thus immune to methods typically used to detect timing based network covert channels.

cs.CR↗

arXiv2014

A Proposed System for Covert Communication to Distant and Broad Geographical Areas

A covert communication system is developed that modulates Morse code characteristics and that delivers its mes- sage economically and to geographically remote areas using radio and EchoLink. Our system allows a covert message to be sent to a receiving individual by hiding it in an existing carrier Morse code message. The carrier need not be sent directly to the receiving person, though the receiver must have access to the signal. Illustratively, we propose that our system may be used as an alternative means of implementing numbers stations.

cs.CR↗

arXiv2014

A Covert Channel Using Named Resources

A network covert channel is created that uses resource names such as addresses to convey information, and that approximates typical user behavior in order to blend in with its environment. The channel correlates available resource names with a user defined code-space, and transmits its covert message by selectively accessing resources associated with the message codes. In this paper we focus on an implementation of the channel using the Hypertext Transfer Protocol (HTTP) with Uniform Resource Locators (URLs) as the message names, though the system can be used in conjunction with a variety of protocols. The covert channel does not modify expected protocol structure as might be detected by simple inspection, and our HTTP implementation emulates transaction level web user behavior in order to avoid detection by statistical or behavioral analysis.

cs.CR↗

arXiv2014

Some Basic Radio System OPSEC Considerations

This is an unscientific introduction to basic radio frequency system OPSEC aspects that I have found to be overlooked and lacking in high security system deployments that may have benefited from them.

cs.CR↗