Showing 1–8 of 8 results for author: Boer, M

Vibrational Circular Dichroism enhancement in conformationally flexible transition metal complexes

Authors: Mariia Sapova, Menno de Boer, Wybren Jan Buma, Lucas Visscher

Abstract: We extend our previously developed approach for calculating enhanced vibrational circular dichroism (VCD) spectra of transition-metal complexes to systems for which conformational flexibility is key to reproduce and elucidate experimental spectra. Treating both the Gibbs free energies and electronic excitation energies as fitting parameters, we show for Co(II)bis[N-(1-arylethyl)- salicylaldiminato… ▽ More We extend our previously developed approach for calculating enhanced vibrational circular dichroism (VCD) spectra of transition-metal complexes to systems for which conformational flexibility is key to reproduce and elucidate experimental spectra. Treating both the Gibbs free energies and electronic excitation energies as fitting parameters, we show for Co(II)bis[N-(1-arylethyl)- salicylaldiminato] Schiff base complexes that these calculations can excellently reproduce the experiment. An important conclusion is that the DFT-optimized conformer set is spectrally redundant and that the model can be reduced from 18 conformers to only two conformers with opposite chirality at the metal center ($Λ$/$Δ$) without affecting the agreement between theory and experiment, both with respect to the VCD spectrum as well population distribution over the $Λ$ and $Δ$ conformers. Finally, we numerically confirm the symmetry-selective nature of the enhancement and formulate the corresponding selection rules within the framework of the pertaining Sum-Over-States expressions. △ Less

Submitted 20 July, 2026; originally announced July 2026.

Ghost State of Light

Authors: R. M. de Boer, C. Toebes, Jan Klars, S. R. K. Rodriguez

Abstract: We report the observation of a long-lived non-stationary state of light in a single-mode optical cavity. The observed state is a ghost of a saddle-node bifurcation which creates a bottleneck in phase space. While such ghosts are known to exist, accessing them is challenging because it requires a mechanism that steers the relaxation pathway away from the true attractor and into the bottleneck where… ▽ More We report the observation of a long-lived non-stationary state of light in a single-mode optical cavity. The observed state is a ghost of a saddle-node bifurcation which creates a bottleneck in phase space. While such ghosts are known to exist, accessing them is challenging because it requires a mechanism that steers the relaxation pathway away from the true attractor and into the bottleneck where the ghost emerges. Here we identify such a mechanism, namely a nonlinear response with memory. Our experimental system leverages this mechanism, enabling us to observe ghost states with lifetimes exceeding the cavity photon lifetime by more than ten orders of magnitude, even in the presence of strong fluctuations. The ghost manifests as a plateau in the relaxation dynamics of the cavity transmission, reminiscent of prethermalization. We show how the ghost lifetime depends on the memory time and the distance to the bifurcation, and we observe signatures of scaling in the distribution of ghost lifetimes at fixed driving conditions. Our work establishes minimal conditions for realizing parametrically long-lived non-stationary states. △ Less

Submitted 13 May, 2026; originally announced May 2026.

Continuous-Wave Nonlinear Polarization Control and Signatures of Criticality in a Perovskite Cavity

Authors: G. Keijsers, R. M. de Boer, B. Verdonschot, K. J. H. Peters, Z. Geng, S. R. K. Rodriguez

Abstract: Halide perovskites have emerged as promising photonic materials for fundamental physics studies and technological applications. Their potential for nonlinear optics has also drawn great interest recently; yet, to date, continuous-wave (CW) nonlinearities have remained elusive. Here we demonstrate CW nonlinear phenomena in a CsPbBr$_3$ perovskite cavity. We first demonstrate optical bistability --… ▽ More Halide perovskites have emerged as promising photonic materials for fundamental physics studies and technological applications. Their potential for nonlinear optics has also drawn great interest recently; yet, to date, continuous-wave (CW) nonlinearities have remained elusive. Here we demonstrate CW nonlinear phenomena in a CsPbBr$_3$ perovskite cavity. We first demonstrate optical bistability -- the hallmark of single-mode coherent nonlinear optics. Next we exploit the interplay of nonlinearity and birefringence to demonstrate nonlinear control over the polarization of light. Finally, by measuring the optical hysteresis of our cavity as a function of temperature, we find a dramatic enhancement of the nonlinearity around 65 K. This enhancement is indicative of a phase transition in CsPbBr$_3$. Our results position CsPbBr$_3$ cavities as an exceptional platform for nonlinear optics, offering strong CW nonlinearity and birefringence which are furthermore tunable. In addition, our approach to uncover a phase transition of matter via optical hysteresis measurements is promising for exploring strongly correlated states of light-matter systems. △ Less

Submitted 8 July, 2024; originally announced July 2024.

Comments: Main: pages 1-11, including 4 figures. Supplemental: pages 12-17, including 10 supplemental figures

Bi-objective optimization of organ properties for the simulation of intracavitary brachytherapy applicator placement in cervical cancer

Authors: Cedric J. Rodriguez, Stephanie M. de Boer, Peter A. N. Bosman, Tanja Alderliesten

Abstract: Validation of deformable image registration techniques is extremely important, but hard, especially when complex deformations or content mismatch are involved. These complex deformations and content mismatch, for example, occur after the placement of an applicator for brachytherapy for cervical cancer. Virtual phantoms could enable the creation of validation data sets with ground truth deformation… ▽ More Validation of deformable image registration techniques is extremely important, but hard, especially when complex deformations or content mismatch are involved. These complex deformations and content mismatch, for example, occur after the placement of an applicator for brachytherapy for cervical cancer. Virtual phantoms could enable the creation of validation data sets with ground truth deformations that simulate the large deformations that occur between image acquisitions. However, the quality of the multi-organ Finite Element Method (FEM)-based simulations is dependent on the patient-specific external forces and mechanical properties assigned to the organs. A common approach to calibrate these simulation parameters is through optimization, finding the parameter settings that optimize the match between the outcome of the simulation and reality. When considering inherently simplified organ models, we hypothesize that the optimal deformations of one organ cannot be achieved with a single parameter setting without compromising the optimality of the deformation of the surrounding organs. This means that there will be a trade-off between the optimal deformations of adjacent organs, such as the vagina-uterus and bladder. This work therefore proposes and evaluates a multi-objective optimization approach where the trade-off between organ deformations can be assessed after optimization. We showcase what the extent of the trade-off looks like when bi-objectively optimizing the patient-specific mechanical properties and external forces of the vagina-uterus and bladder for FEM-based simulations. △ Less

Submitted 22 February, 2023; originally announced March 2023.

Maximum likelihood analysis of non-equilibrium solution-based single-molecule FRET data

Authors: Marijn de Boer

Abstract: Measuring the Förster resonance energy transfer (FRET) efficiency of freely diffusing single molecules provides information about the sampled conformational states of the molecules. Under equilibrium conditions, the distribution of the conformational states is independent of time, whereas it can vary over time under non-equilibrium conditions. In this work, we consider the problem of parameter inf… ▽ More Measuring the Förster resonance energy transfer (FRET) efficiency of freely diffusing single molecules provides information about the sampled conformational states of the molecules. Under equilibrium conditions, the distribution of the conformational states is independent of time, whereas it can vary over time under non-equilibrium conditions. In this work, we consider the problem of parameter inference on non-equilibrium solution-based single-molecule FRET data. With a non-equilibrium model for the conformational dynamics and a model for the conformation-dependent FRET efficiency distribution, the likelihood function could be constructed. The model parameters, such as the rate constants of the non-equilibrium conformational dynamics model and the average FRET efficiencies of the different conformational states, have been estimated from the data by maximizing the appropriate likelihood function via the Expectation-Maximization algorithm. We illustrate the likelihood method for a few simple non-equilibrium models and validated the method by simulations. The likelihood method could be applied to study protein folding, macromolecular complex formation, protein conformational dynamics and other non-equilibrium processes at the single-molecule level and in solution. △ Less

Submitted 27 August, 2020; originally announced August 2020.

The COMPASS Setup for Physics with Hadron Beams

Authors: Ph. Abbon, C. Adolph, R. Akhunzyanov, Yu. Alexandrov, M. G. Alexeev, G. D. Alexeev, A. Amoroso, V. Andrieux, V. Anosov, A. Austregesilo, B. Badelek, F. Balestra, J. Barth, G. Baum, R. Beck, Y. Bedfer, A. Berlin, J. Bernhard, K. Bicker, E. R. Bielert, J. Bieling, R. Birsa, J. Bisplinghoff, M. Bodlak, M. Boer , et al. (207 additional authors not shown)

Abstract: The main characteristics of the COMPASS experimental setup for physics with hadron beams are described. This setup was designed to perform exclusive measurements of processes with several charged and/or neutral particles in the final state. Making use of a large part of the apparatus that was previously built for spin structure studies with a muon beam, it also features a new target system as well… ▽ More The main characteristics of the COMPASS experimental setup for physics with hadron beams are described. This setup was designed to perform exclusive measurements of processes with several charged and/or neutral particles in the final state. Making use of a large part of the apparatus that was previously built for spin structure studies with a muon beam, it also features a new target system as well as new or upgraded detectors. The hadron setup is able to operate at the high incident hadron flux available at CERN. It is characterised by large angular and momentum coverages, large and nearly flat acceptances, and good two and three-particle mass resolutions. In 2008 and 2009 it was successfully used with positive and negative hadron beams and with liquid hydrogen and solid nuclear targets. This article describes the new and upgraded detectors and auxiliary equipment, outlines the reconstruction procedures used, and summarises the general performance of the setup. △ Less

Submitted 7 October, 2014; originally announced October 2014.

Comments: 91 pages, 101 figures and 7 tables

Advanced Virgo: a 2nd generation interferometric gravitational wave detector

Authors: F. Acernese, M. Agathos, K. Agatsuma, D. Aisa, N. Allemandou, A. Allocca, J. Amarni, P. Astone, G. Balestri, G. Ballardin, F. Barone, J. -P. Baronick, M. Barsuglia, A. Basti, F. Basti, Th. S. Bauer, V. Bavigadda, M. Bejger, M. G. Beker, C. Belczynski, D. Bersanetti, A. Bertolini, M. Bitossi, M. A. Bizouard, S. Bloemen , et al. (209 additional authors not shown)

Abstract: Advanced Virgo is the project to upgrade the Virgo interferometric detector of gravitational waves, with the aim of increasing the number of observable galaxies (and thus the detection rate) by three orders of magnitude. The project is now in an advanced construction phase and the assembly and integration will be completed by the end of 2015. Advanced Virgo will be part of a network with the two A… ▽ More Advanced Virgo is the project to upgrade the Virgo interferometric detector of gravitational waves, with the aim of increasing the number of observable galaxies (and thus the detection rate) by three orders of magnitude. The project is now in an advanced construction phase and the assembly and integration will be completed by the end of 2015. Advanced Virgo will be part of a network with the two Advanced LIGO detectors in the US and GEO HF in Germany, with the goal of contributing to the early detections of gravitational waves and to opening a new observation window on the universe. In this paper we describe the main features of the Advanced Virgo detector and outline the status of the construction. △ Less

Submitted 16 October, 2014; v1 submitted 18 August, 2014; originally announced August 2014.

Comments: Submitted to Classical and Quantum Gravity. 55 pages, 29 figures

Journal ref: Class. Quantum Grav. 32 (2015) 024001

Reconstruction of the gravitational wave signal $h(t)$ during the Virgo science runs and independent validation with a photon calibrator

Authors: Virgo collaboration, T. Accadia, F. Acernese, M. Agathos, A. Allocca, P. Astone, G. Ballardin, F. Barone, M. Barsuglia, A. Basti, Th. S. Bauer, M. Bejger, M . G. Beker, C. Belczynski, D. Bersanetti, A. Bertolini, M. Bitossi, M. A. Bizouard, M. Blom, M. Boer, F. Bondu, L. Bonelli, R. Bonnand, V. Boschi, L. Bosi , et al. (171 additional authors not shown)

Abstract: The Virgo detector is a kilometer-scale interferometer for gravitational wave detection located near Pisa (Italy). About 13 months of data were accumulated during four science runs (VSR1, VSR2, VSR3 and VSR4) between May 2007 and September 2011, with increasing sensitivity. In this paper, the method used to reconstruct, in the range 10 Hz-10 kHz, the gravitational wave strain time series $h(t)$… ▽ More The Virgo detector is a kilometer-scale interferometer for gravitational wave detection located near Pisa (Italy). About 13 months of data were accumulated during four science runs (VSR1, VSR2, VSR3 and VSR4) between May 2007 and September 2011, with increasing sensitivity. In this paper, the method used to reconstruct, in the range 10 Hz-10 kHz, the gravitational wave strain time series $h(t)$ from the detector signals is described. The standard consistency checks of the reconstruction are discussed and used to estimate the systematic uncertainties of the $h(t)$ signal as a function of frequency. Finally, an independent setup, the photon calibrator, is described and used to validate the reconstructed $h(t)$ signal and the associated uncertainties. The uncertainties of the $h(t)$ time series are estimated to be 8% in amplitude. The uncertainty of the phase of $h(t)$ is 50 mrad at 10 Hz with a frequency dependence following a delay of 8 $μ$s at high frequency. A bias lower than $4\,\mathrm{μs}$ and depending on the sky direction of the GW is also present. △ Less

Submitted 3 July, 2014; v1 submitted 23 January, 2014; originally announced January 2014.

Comments: 35 pages, 16 figures. Accepted by CQG

Journal ref: T Accadia et al 2014 Class. Quantum Grav. 31 165013