arXiv subjects

Christian Merz

Publications and source records attributed to Christian Merz.

5 recordsLinked to original sources

arXiv2026

Technological Advances in Two Generations of Consumer-Grade VR Systems: Effects on User Experience and Task Performance

Integrated VR (IVR) systems consist of a head-mounted display (HMD) and body-tracking capabilities. They enable users to translate their physical movements into corresponding avatar movements in real-time, allowing them to perceive their avatars via the displays. Consumer-grade IVR systems have been available for 10 years, significantly fostering VR research worldwide. However, the effects of even apparently significant technological advances of IVR systems on user experience and the overall validity of prior embodiment research using such systems often remain unclear. We ran a user-centered study comparing two comparable IVR generations: a nearly 10-year-old hardware (HTC Vive, 6-point tracking) and a modern counterpart (HTC Vive Pro 2, 6-point tracking). To ensure ecological validity, we evaluated the systems in their commercially available, as-is configurations. In a 2x5 mixed design, participants completed five tasks covering different use cases on either the old or new system. We assessed presence, sense of embodiment, appearance and behavior plausibility, workload, task performance, and gathered qualitative feedback. Results showed no significant system differences, with only small effect sizes. Bayesian analysis further supported the null hypothesis, suggesting that the investigated generational hardware improvements offer limited benefits for user experience and task performance. For the 10-year generational step examined here, excluding potential technological progress in the necessary software components, this supports the validity of conclusions from prior work and underscores the applicability of older configurations for research in embodied VR.

cs.HC↗

arXiv2025

Building AI-based advisory services for smallholder farmers: Technical learnings from the AIEP Initiative

We report technical learnings from five AI-based agricultural advisory MVPs deployed in Kenya and Bihar, India, under the AIEP Initiative. A 800-farmer study found high user satisfaction (NPS ~60). All solutions implement a modular two-part architecture: (i) an interface component (IVR /WhatsApp / app) with ASR-MT-TTS for multilingual voice access; and (ii) a reasoning component combining LLMs capabilities with query orchestration, external data (weather/soil/markets), and RAG over curated agricultural corpora. We describe key challenges: (a) latency, especially for voice; reductions were achieved via in-country hosting and audio minimization, but consistent <5s remains challenging; (b) language coverage: low-resource ASR/MT integration and nonstandard scripts hinder end-to-end quality; and (c) corpus curation: access, validation, and maintenance are labor-intensive, as well as provide recommendations on how to develop similar systems. We discuss common enablers including (a) data sharing, (b) common corpora, (c) better language AI and (d) evaluation and benchmarking. We also present golden Q&A sets to evaluate LLM capabilities for smallholder agriculture.

cs.HC↗

arXiv2025

Unobtrusive In-Situ Measurement of Behavior Change by Deep Metric Similarity Learning of Motion Patterns

This paper introduces an unobtrusive in-situ measurement method to detect user behavior changes during arbitrary exposures in XR systems. Here, such behavior changes are typically associated with the Proteus effect or bodily affordances elicited by different avatars that the users embody in XR. We present a biometric user model based on deep metric similarity learning, which uses high-dimensional embeddings as reference vectors to identify behavior changes of individual users. We evaluate our model against two alternative approaches: a (non-learned) motion analysis based on central tendencies of movement patterns and subjective post-exposure embodiment questionnaires frequently used in various XR exposures. In a within-subject study, participants performed a fruit collection task while embodying avatars of different body heights (short, actual-height, and tall). Subjective assessments confirmed the effective manipulation of perceived body schema, while the (non-learned) objective analyses of head and hand movements revealed significant differences across conditions. Our similarity learning model trained on the motion data successfully identified the elicited behavior change for various query and reference data pairings of the avatar conditions. The approach has several advantages in comparison to existing methods: 1) In-situ measurement without additional user input, 2) generalizable and scalable motion analysis for various use cases, 3) user-specific analysis on the individual level, and 4) with a trained model, users can be added and evaluated in real time to study how avatar changes affect behavior.

cs.HC↗

arXiv2025

RL2Grid: Benchmarking Reinforcement Learning in Power Grid Operations

Reinforcement learning (RL) can provide adaptive and scalable controllers essential for power grid decarbonization. However, RL methods struggle with power grids' complex dynamics, long-horizon goals, and hard physical constraints. For these reasons, we present RL2Grid, a benchmark designed in collaboration with power system operators to accelerate progress in grid control and foster RL maturity. Built on RTE France's power simulation framework, RL2Grid standardizes tasks, state and action spaces, and reward structures for a systematic evaluation and comparison of RL algorithms. Moreover, we integrate operational heuristics and design safety constraints based on human expertise to ensure alignment with physical requirements. By establishing reference performance metrics for classic RL baselines on RL2Grid's tasks, we highlight the need for novel methods capable of handling real systems and discuss future directions for RL-based grid control.

cs.LG↗

arXiv2025

Accelerated DC loadflow solver for topology optimization

We present a massively parallel solver that accelerates DC loadflow computations for power grid topology optimization tasks. Our approach leverages low-rank updates of the Power Transfer Distribution Factors (PTDFs) to represent substation splits, line outages, and reconfigurations without ever refactorizing the system. Furthermore, we implement the core routines on Graphics Processing Units (GPUs), thereby exploiting their high-throughput architecture for linear algebra. A two-level decomposition separates changes in branch topology from changes in nodal injections, enabling additional speed-ups by an in-the-loop brute force search over injection variations at minimal additional cost. We demonstrate billion-loadflow-per-second performance on power grids of varying sizes in workload settings which are typical for gradient-free topology optimization such as Reinforcement Learning or Quality Diversity methods. While adopting the DC approximation sacrifices some accuracy and prohibits the computation of voltage magnitudes, we show that this sacrifice unlocks new scales of computational feasibility, offering a powerful tool for large-scale grid planning and operational topology optimization.

eess.SY↗