Embedded Files
Talks
Talks
Invited talks
Zero-shot sampling of adversarial entities in biomedical question answering (jointly with Reza Abbasi-Asl), Information Theory and Applications 2024, UCSD, San Diego, CA, USA (2024)
The meaningful scales and how we reach there – from solid materials to organs, University of Erlangen-Nürnberg, Erlangen, Germany (virtual, 2021)
Towards materials data science – where high-throughput computation will meet high-throughput experimentation, Fritz Haber Institute of the Max Planck Society, Berlin, Germany (virtual, 2020)
Challenges and opportunities in multidimensional photoemission spectroscopy (MPES) data analysis, Max Planck Institute for Intelligent Systems, Tübingen, Germany (2018)
Challenges and opportunities in multidimensional photoemission spectroscopy (MPES) data analysis, Max Planck Institute of Colloids and Interfaces, Potsdam-Golm, Germany (2018)
Multidimensional photoemission spectroscopy (joint with R. Ernstorfer), BiGmax Workshop on Big-Data-Driven Materials Science, Kloster Irsee, Germany (2018)
Atomically-resolved structural changes during a solid state geminate recombination reaction, 20th International Conference on Ultrafast Phenomena, Santa Fe, New Mexico, USA (2016)
Crystalline phase geminate recombination of triiodide investigated with ultrafast time-resolved electron diffraction, 45th IUPAC World Chemistry Congress, Busan, South Korea (2015)
Other talks
Data-driven approaches to photoemission spectroscopy, Fritz Haber Institute Physical Chemistry Department Retreat, Hotel Griebnitzsee, Potsdam, Germany (2018)
What can we learn from time-resolved ARPES (trARPES) data? Fritz Haber Institute Physical Chemistry Department Retreat, Schloss Ringberg, Germany (2017)
Conferences & Workshops
Conferences & Workshops
As a co-host or co-organizer
Satellite workshop co-host, Conference on a FAIR data infrastructure for materials genomics, Berlin, Germany (virtual, 2020)
First-authored posters
Inherent and emergent liability issues in LLM-based agentic systems: a principal-agent perspective, REALM Workshop, Annual Meeting of the Association for Computational Linguistics, Vienna, Austria (2025)
Measuring temporal effects of agent knowledge by date-controlled tool use, REALM Workshop, Annual Meeting of the Association for Computational Linguistics, Vienna, Austria (2025)
Gigascale electron event processing for band structure mapping, BiGmax Workshop, Potsdam, Germany (virtual, 2021)
Feature-preserving image symmetrization for electron momentum microscopy, Sculpted Light in the Brain, London, UK (2019)
Multidimensional photoemission spectroscopy data: A framework for distributed and volumetric processing, German Physical Society Spring Meeting, Regensburg, Germany (2019)
Photochemistry of the triiodide anion captured by femtosecond electron diffraction, 21th International Conference on Ultrafast Phenomena, Hamburg, Germany (2018)
Momentum-resolved hole and exciton dynamics in WSe2, German Physical Society Spring Meeting, Berlin, Germany (2018)
5th Banff Meeting on Structural Dynamics, Banff, British Columbia, Canada (2017)
Vibrationally resolved geminate recombination of solid state triiodide using ultrafast electron diffraction, 12th Femtochemistry Conference (Femto12), Hamburg, Germany (2015)
Coherent control of the photodissociation of triiodide in solution reveals new pathways, 19th International Conference on Ultrafast Phenomena, Okinawa, Japan (2014)
Publications
Publications
Conference proceedings (* = equal contribution)
G. A. Gabison*, R. P. Xian*, Inherent and emergent liability issues in LLM-based agentic systems: a principal-agent perspective, The First Workshop for Research on Agent Language Models (REALM), ACL 2025 [arXiv:2504.03255].
A comprehensive overview of liability issues in LLM agents and their extended software platforms and promising technical dimensions needed to govern the agent ecosystem.
R. P. Xian, Q. Cui, S. Bauer, R. Abbasi-Asl, Measuring temporal effects of agent knowledge by date-controlled tool use, The First Workshop for Research on Agent Language Models (REALM), ACL 2025 [arXiv:2503.04188].
R. Xian, S. A. Hayes, G. Corthey, C. A. Morrison, A. Marx, V. I. Prokhorenko, C. Lu, R. J. D. Miller Towards understanding of the triiodide anion photochemistry in solid state by femtosecond electron diffraction, Ultrafast Phenomena XXI, EPJ Web of Conf. 205, 09007 (2019).
R. Xian, G. Corthey, S. A. Hayes, C. A. Morrison, D. M. Rogers, A. Marx, V. I. Prokhorenko, C. Lu, R. J. D. Miller, Towards atomically-Resolved Structural Changes during a Solid State Geminate Recombination Reaction, Ultrafast Phenomena XX, UTh2B. 1 (2016).
R. Xian, V. I. Prokhorenko, R. L. Field, R. J. D. Miller, Coherent control of the photodissociation of triiodide in solution reveals new pathways, Ultrafast Phenomena XIX, 382 (2015).
Journal publications + preprints (* = equal contribution)
R. P. Xian, N. R. Baker, T. David, Q. Cui, A. J. Holmgren, S. Bauer, M. Sushil, R. Abbasi-Asl, Robustness tests for biomedical foundation models should tailor to specifications, in press [SSRN: 10.2139/ssrn.5013799][arXiv:2502.10374]
R. P. Xian*, S. A. Hayes*, G. Corthey, C. A. Morrison, A. Marx, H. Daoud, C. Lu, R. J. D. Miller, Atomic Trajectories of a Bimolecular Reaction Visualized by Ultrafast Electron Diffraction, Journal of the American Chemical Society (2025) [ChemRxiv: 10.26434/chemrxiv-2025-j2m79]
R. P. Xian, A. J. Lee, S. Lolla, V. Wang, Q. Cui, R. Ro, R. Abbasi-Asl, Assessing biomedical knowledge robustness in large language models by query-efficient sampling attacks, Transactions on Machine Learning Research (2024) [OpenReview link][arXiv: 2402.10527v2].
Unified embedding space sampling and search framework for probing large language models' biomedical knowledge robustness.
R. Cahill*, Y. Wang*, R. P. Xian, A. J. Lee, H. Zeng, B. Yu, B. Tasic, R. Abbasi-Asl, Unsupervised pattern identification in spatial gene expression atlas reveals mouse brain regions beyond established ontology, Proceedings of the National Academy of Sciences 121 (37), e2319804121 (2024) [biorxiv:10.1101/2023.03.10.531984v2].
Stability-driven matrix factorization meets spatial analysis for interpretable transcriptomics analysis in 3D.
R. P. Xian*, J. Brunet*, Y. Huang, W. L. Wagner, P. D. Lee, P. Tafforeau, C. L. Walsh, A closer look at high-energy X-ray-induced bubble formation during soft tissue imaging, Journal of Synchrotron Radiation 31, 566 (2024) [biorxiv:10.1101/2023.02.14.528474].
R. P. Xian, R. J. Morelock, I. Hadar, C. B. Musgrave, C. Sutton, From structure mining to unsupervised exploration of atomic octahedral networks [arXiv:2306.12272].
A.. Neef, S. Beaulieu, S. Hammer, S. Dong, J. Makler, T. Pincelli, R. P. Xian, M. Wolf, L. Rettig, J. Pflaum, R. Ernstorfer, Orbital-resolved observation of singlet fission, Nature 616, 275 (2023) [arXiv:2204.06824].
T. Pincelli*, T. Vasileiadis*, S. Dong, S. Beaulieu, M. Dendzik, D. Zahn, S.‐E. Lee, H. Seiler, Y. Qi, R. P. Xian, J. Maklar, E. Coy, N. S. Mueller, Y. Okamura, S. Reich, M. Wolf, L. Rettig, R. Ernstorfer, Observation of Multi‐Directional Energy Transfer in a Hybrid Plasmonic‐Excitonic Nanostructure, Advanced Materials 35, 2209100 (2023) [arXiv:2211.04615].
R. P. Xian*, V. Stimper*, M. Zacharias, S. Dong, M. Dendzik, S. Beaulieu, B. Schölkopf, M.Wolf, L. Rettig, C. Carbogno, S. Bauer, R. Ernstorfer, A machine learning route between band mapping and band structure, Nature Computational Science 3, 101 (2023) [arXiv:2005.10210].
First efficient machine learning reconstruction algorithm for multidimensional (electronic) dispersion surfaces.
R. P. Xian*, C. L. Walsh, S. Verleden, W. L. Wagner, A. Bellier, S. Marussi, J. Jacob, M. Ackermann, D. D. Jonigk, P. D. Lee, P. Tafforeau*, A multiscale X-ray phase-contrast tomography dataset of a whole human left lung, Scientific Data 9, 264 (2022) [bioRxiv:10.1101/2021.11.20.469361].
To-date the largest and structurally most comprehensive X-ray imaging dataset for an entire human lung.
S. Dong, S. Beaulieu, M. Selig, P. Rosenzweig, D. Christiansen, T. Pincelli, M. Dendzik, J. D. Ziegler, J. Maklar, R. P. Xian, A. Neef, A. Mohammed, A. Schulz, M. Stadler, M. Jetter, P. Michler, T. Taniguchi, K. Watanabe, H. Takagi, U. Starke, A. Chernikov, M. Wolf, H. Nakamura, A. Knorr, L. Rettig, R. Ernstorfer, Observation of ultrafast interfacial Meitner-Auger energy transfer in a van der Waals heterostructure, Nature Communications 14, 5057 (2023) [arXiv:2108.06803].
M. Puppin, C. W. Nicholson, C. Monney, Y. Deng, R. P. Xian, J. Feldl, S. Dong, A. Dominguez, H. Hübener, A. Rubio, M. Wolf, L. Rettig, R. Ernstorfer, Excited state band structure mapping, Physical Review B 105, 075417 (2022) [arXiv:2108.07099].
Demonstration of improved signal statistics in mapping excited-state electronic structure using a high-repetition-rate extreme UV source.
Z. Chen*, N. Andrejevic*, N. Drucker, T. Nguyen, R. P. Xian, T. Smidt, Y. Wang, R. Ernstorfer, A. Tennant, M. Chan, M. Li, Machine learning on neutron and X-Ray scattering, Chemical Physics Reviews, 2, 031301 (2021) [arXiv:2102.03024].
First comprehensive review on machine learning contexts and tasks for X-ray and neutron experiments.
M. Du, Z. Di, D. Güsoy, R. P. Xian, Y. Kozorovitskiy, C. Jacobsen, Upscaling X-ray nanoimaging for macroscopic specimens, Journal of Applied Crystallography 54, 386 (2021).
A perspective on the nuts and bolts of whole-brain connectomics with dense, high-resolution, large-scale X-ray imaging.
R. P. Xian, R. Ernstorfer, P. M. Pelz, Scalable multicomponent spectral analysis for high-throughput data annotation, [arXiv:2102.05604].
A universal mapping of multidimensional spectral fitting task to distributed computing resources.
S. Dong*, M. Puppin*, T. Pincelli, S. Beaulieu, D. Christiansen, H. Hubener, C. W. Nicholson, R. P. Xian, M. Dendzik, Y. Deng, Y. W. Windsor, M. Selig, E. Malic, A. Rubio, A. Knorr, M. Wolf, L. Rettig, R. Ernstorfer, Direct measurement of key exciton properties: energy, dynamics and spatial distribution of the wave function, Natural Sciences, e10010 (2021) [arXiv:2012.15328].
S. Beaulieu, S. Dong, N. Tancogne-Dejean, M. Dendzik, T. Pincelli, J. Maklar, R. P. Xian, M. A. Sentef, M. Wolf, A. Rubio, L. Rettig, R. Ernstorfer, Ultrafast dynamical Lifshitz transition, Science Advances 7: eabd9275 (2021) [arXiv:2003.04059].
First demonstration of a light-induced, nonthermal Lifshitz phase transition on the ultrafast timescale.
J. Maklar, S. Dong, S. Beaulieu, T. Pincelli, M. Dendzik, Y.W. Windsor, R. P. Xian, M. Wolf, R. Ernstorfer, L. Rettig, A quantitative comparison of time-of-flight momentum microscopes and hemispherical analyzers for time-resolved ARPES experiments, Review of Scientific Instruments 91, 123112 (2020) [arXiv:2008.05829].
M. Dendzik, R. P. Xian, E. Perfetto, D. Sangalli, D. Kutnyakhov, S. Dong, S. Beaulieu, T. Pincelli, F. Pressacco, D. Curcio, S. Y. Agustsson, M. Heber, J. Hauer, W. Wurth, G. Brenner, Y. Acremann, P. Hofmann, M. Wolf, A. Marini, G. Stefanucci, L. Rettig, R. Ernstorfer, Observation of an excitonic Mott transition through ultrafast core-cum-conduction photoemission spectroscopy, Physical Review Letters 125, 096401 (2020) [arXiv:2003.12925].
First empirical demonstration and theoretical modeling of nonequilibrium core-level electron dynamics
R. P. Xian, Y. Acremann, S. Y. Agustsson, M. Dendzik, K. Bühlmann, D. Curcio, D. Kutnyakhov, F. Pressacco, M. Heber, S. Dong, J. Demsar, W. Wurth, P. Hofmann, M. Wolf, L. Rettig, R. Ernstorfer, An open-source, distributed workflow for band mapping data in multidimensional photoemission spectroscopy, Scientific Data 7:442 (2020) [arXiv:1909.07714][Code1][Code2][Code3].
A distributed computational workflow for processing billion-count electron event data and the data standards.
M. Puppin, S. Polishchuk, N. Colonna, A. Crepaldi, D. N. Dirin, O. Nazarenko, R. De Gennaro, G. Gatti, S. Roth, T. Barillot, L. Poletto, R. P. Xian, L. Rettig, M. Wolf, R. Ernstorfer, M. V. Kovalenko, N. Marzari, M. Grioni, M. Chergui, Evidence of large polarons in photoemission band mapping of the perovskite semiconductor CsPbBr3, Physical Review Letters 124, 206402 (2020) [arXiv:1909.00248].
First evidence of large polarons in a model inorganic lead-halide perovskite (CsPbBr3).
D. Kutnyakhov, R. P. Xian, M. Dendzik, M. Heber, F. Pressacco, S. Y. Agustsson, L. Wenthaus, H. Meyer, S. Gieschen, G. Mercurio, A. Benz, K. Bühlman, S. Däster, R. Gort, D. Curcio, K. Volckaert, M. Bianchi, C. Sanders, J. A. Miwa, S. Ulstrup, A. Oelsner, C. Tusche, Y.-J. Chen, D. Vasilyev, K. Medjanik, G. Brenner, S. Dziarzhytski, H. Redlin, B. Manschwetus, S. Dong, J. Hauer, L. Rettig, F. Diekmann, K. Rossnagel, J. Demsar, H.-J. Elmers, Ph. Hofmann, R. Ernstorfer, G. Schönhense, Y. Acremann, W. Wurth, Time- and momentum-resolved photoemission studies using time-of-flight momentum microscopy at a free-electron laser, Review of Scientific Instruments 91, 013109 (2020) [arXiv:1906.12155].
First demonstration of the capabilities of 4D detection of photoemission at a free-electron laser source.
V. Stimper*, S. Bauer, R. Ernstorfer, B. Schölkopf, R. P. Xian*, Multidimensional contrast limited adaptive histogram equalization, IEEE Access, 7, 165437 (2019) [arXiv:1906.11355][Code].
Extension of the CLAHE contrast enhancement algorithm to arbitrary dimensions along with computational speed-up and customization.
R. P. Xian, L. Rettig, R. Ernstorfer, Symmetry-guided nonrigid registration: The case for distortion correction in multidimensional photoemission spectroscopy, Ultramicroscopy, 202, 133 (2019) [arXiv:1901.00312] [Code].
A class of landmark-based iterative symmetry distortion correction algorithms for image data.
R. Xian, G. Corthey, D. M. Rogers, C. A. Morrison, V. I. Prokhorenko, S. A. Hayes, R. J. D. Miller, Coherent ultrafast lattice-directed reaction dynamics of triiodide anion photodissociation, Nature Chemistry 9, 516 (2017).
First report of the course of a solid-state bimolecular photoreaction on subpicosecond timescale, tracked using multispectral detection and adaptive time-frequency analysis.
K. M. Siddiqui, G. Corthey, S. A. Hayes, A. Rossos, D. S. Badali, R. Xian, R. S. Murphy, B. J. Whitaker, R. J. D. Miller, Synchronised photoreversion of spirooxazine ring opening in thin crystals to uncover ultrafast dynamics, CrystEngComm 18, 7212 (2016).
First demonstration of a way to improve sample recovery in solid-state photochemistry using photoreversion pulses synched to excitation.
X.-H. Chen, I. N. Agafonov, K.-H. Luo, Q. Liu, R. Xian, M. V. Chekhova, L.-A. Wu, High visibility, high-order lensless ghost imaging with thermal light, Optics Letters 35, 1166 (2010) [arXiv:0902.3713].
Datasets
Datasets
R. P. Xian, J. Brunet, Y. Huang, W. L. Wagner, P. D. Lee, P. Tafforeau, C. L. Walsh, A closer look at high-energy X-ray-induced bubble formation during soft tissue imaging, Zenodo 10.5281/zenodo.7760251.
P. Tafforeau, C. L. Walsh, W. L. Wagner, R. P. Xian, S. E. Verleden, D. J. Jafree, A. Bellier, C. Werlein, M. P. Kühnel, E. Boller, S. Walker-Samuel, J. L. Robertus, D. A. Long, J. Jacob, S. Marussi, E. Brown, N. Holroyd, D. D. Jonigk, M. Ackermann, P. D. Lee, A multiscale X-ray phase-contrast tomography dataset of whole human left lung, Human Organ Atlas HOA-LADAF-27-lung.
S. Dong, M. Puppin, T. Pincelli, S. Beaulieu, D. Christiansen, H. Hübener, C. W. Nicholson, R. P. Xian, M. Dendzik, Y. Deng, Y. W. Windsor, M. Selig, E. Malic, A. Rubio, A. Knorr, M. Wolf, L. Rettig, R Ernstorfer, Direct measurement of key exciton properties: energy, dynamics and spatial distribution of the wave function, Zenodo 10.5281/zenodo.4739194.
M. Puppin, S. Polishchuk, N. Colonna, A. Crepaldi, D. N. Dirin, O. Nazarenko, R. De Gennaro, G. Gatti, S. Roth, T. Barillot, L. Poletto, R. P. Xian, L. Rettig, M. Wolf, R. Ernstorfer, M. V. Kovalenko, N. Marzari, M. Grioni, M. Chergui, Evidence of large polarons in photoemission band mapping of the perovskite semiconductor CsPbBr3, Materials Cloud 10.24435/materialscloud:gb-90.
J. Maklar, S. Dong, S. Beaulieu, T. Pincelli, M. Dendzik, Y. W. Windsor, R. P. Xian, M. Wolf, R. Ernstorfer, L. Rettig, Time-resolved ARPES data of bulk WSe2 for a quantitative comparison of time-of-flight momentum microscopes and hemispherical analyzers, Zenodo 10.5281/zenodo.4067967.
R. P. Xian, Y. Acremann, S. Y. Agustsson, M. Dendzik, K. Bühlmann, D. Curcio, D. Kutnyakhov, F. Pressacco, M. Heber, S. Dong, T. Pincelli, J. Demsar, W. Wurth, Ph. Hofmann, M. Wolf, M. Scheidgen, L. Rettig, R. Ernstorfer, Datasets for the computational workflow of multidimensional photoemission spectroscopy, Zenodo 10.5281/zenodo.3987303.
M. Dendzik, R. P. Xian, E. Perfetto, D. Sangalli, D. Kutnyakhov, S. Dong, S. Beaulieu, T. Pincelli, F. Pressacco, D. Curcio, S. Y. Agustsson, M. Heber, J. Hauer, W. Wurth, G. Brenner, Y. Acremann, P. Hofmann, M. Wolf, A. Marini, G. Stefanucci, L. Rettig, R. Ernstorfer, Zenodo 10.5281/zenodo.3945433.
R. P. Xian, D. Kutnyakhov, L. Rettig, Y. Acremann, F. Pressacco, S. Y. Agustsson, D. Curcio, M. Dendzik, G. Brenner, H. Redlin, M. Heber, G. Mercurio, S. Dong, J. Hauer, J. Demsar, W. Wurth, Ph. Hofmann, M. Scheidgen, R. Ernstorfer, Multidimensional photoemission spectra of tungsten diselenide, Zenodo 10.5281/zenodo.2704787.
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