Professional Education

  • Diplom, Technische Universität Berlin, Physics (2012)
  • Dr. rer. nat, Humboldt-Universität zu Berlin, Theoretical Physics (2016)

Lab Affiliations

All Publications

  • Chemokinetic Scattering, Trapping, and Avoidance of Active Brownian Particles PHYSICAL REVIEW LETTERS Kromer, J. A., de la Cruz, N., Friedrich, B. M. 2020; 124 (11)
  • Long-lasting desynchronization by decoupling stimulation PHYSICAL REVIEW RESEARCH Kromer, J. A., Tass, P. A. 2020; 2 (3)
  • Impact of number of stimulation sites on long-lasting desynchronization effects of coordinated reset stimulation CHAOS Kromer, J. A., Khaledi-Nasab, A., Tass, P. A. 2020; 30

    View details for DOI 10.1063/5.0015196

  • Variability of collective dynamics in random tree networks of strongly coupled stochastic excitable elements PHYSICAL REVIEW E Khaledi-Nasab, A., Kromer, J. A., Schimansky-Geier, L., Neiman, A. B. 2018; 98 (5)
  • General solution of the chemical master equation and modality of marginal distributions for hierarchic first-order reaction networks JOURNAL OF MATHEMATICAL BIOLOGY Reis, M., Kromer, J. A., Klipp, E. 2018; 77 (2): 377–419


    Multimodality is a phenomenon which complicates the analysis of statistical data based exclusively on mean and variance. Here, we present criteria for multimodality in hierarchic first-order reaction networks, consisting of catalytic and splitting reactions. Those networks are characterized by independent and dependent subnetworks. First, we prove the general solvability of the Chemical Master Equation (CME) for this type of reaction network and thereby extend the class of solvable CME's. Our general solution is analytical in the sense that it allows for a detailed analysis of its statistical properties. Given Poisson/deterministic initial conditions, we then prove the independent species to be Poisson/binomially distributed, while the dependent species exhibit generalized Poisson/Khatri Type B distributions. Generalized Poisson/Khatri Type B distributions are multimodal for an appropriate choice of parameters. We illustrate our criteria for multimodality by several basic models, as well as the well-known two-stage transcription-translation network and Bateman's model from nuclear physics. For both examples, multimodality was previously not reported.

    View details for DOI 10.1007/s00285-018-1205-2

    View details for Web of Science ID 000439442300004

    View details for PubMedID 29353313

    View details for PubMedCentralID PMC6061068

  • Decision making improves sperm chemotaxis in the presence of noise PLOS COMPUTATIONAL BIOLOGY Kromer, J. A., Maercker, S., Lange, S., Baier, C., Friedrich, B. M. 2018; 14 (4): e1006109


    To navigate their surroundings, cells rely on sensory input that is corrupted by noise. In cells performing chemotaxis, such noise arises from the stochastic binding of signalling molecules at low chemoattractant concentrations. We reveal a fundamental relationship between the speed of chemotactic steering and the strength of directional fluctuations that result from the amplification of noise in a chemical input signal. This relation implies a trade-off between steering that is slow and reliable, and steering that is fast but less reliable. We show that dynamic switching between these two modes of steering can substantially increase the probability to find a target, such as an egg to be found by sperm cells. This decision making confers no advantage in the absence of noise, but is beneficial when chemical signals are detectable, yet characterized by low signal-to-noise ratios. The latter applies at intermediate distances from a target, where signalling molecules are diluted, thus defining a 'noise zone' that cells have to cross. Our results explain decision making observed in recent experiments on sea urchin sperm chemotaxis. More generally, our theory demonstrates how decision making enables chemotactic agents to cope with high levels of noise in gradient sensing by dynamically adjusting the persistence length of a biased random walk.

    View details for DOI 10.1371/journal.pcbi.1006109

    View details for Web of Science ID 000432169600044

    View details for PubMedID 29672515

    View details for PubMedCentralID PMC5929576

  • Emergent stochastic oscillations and signal detection in tree networks of excitable elements SCIENTIFIC REPORTS Kromer, J., Khaledi-Nasab, A., Schimansky-Geier, L., Neiman, A. B. 2017; 7: 3956


    We study the stochastic dynamics of strongly-coupled excitable elements on a tree network. The peripheral nodes receive independent random inputs which may induce large spiking events propagating through the branches of the tree and leading to global coherent oscillations in the network. This scenario may be relevant to action potential generation in certain sensory neurons, which possess myelinated distal dendritic tree-like arbors with excitable nodes of Ranvier at peripheral and branching nodes and exhibit noisy periodic sequences of action potentials. We focus on the spiking statistics of the central node, which fires in response to a noisy input at peripheral nodes. We show that, in the strong coupling regime, relevant to myelinated dendritic trees, the spike train statistics can be predicted from an isolated excitable element with rescaled parameters according to the network topology. Furthermore, we show that by varying the network topology the spike train statistics of the central node can be tuned to have a certain firing rate and variability, or to allow for an optimal discrimination of inputs applied at the peripheral nodes.

    View details for DOI 10.1038/s41598-017-04193-8

    View details for Web of Science ID 000403840000028

    View details for PubMedID 28638071

    View details for PubMedCentralID PMC5479816

  • Emergence and coherence of oscillations in star networks of stochastic excitable elements PHYSICAL REVIEW E Kromer, J. A., Schimansky-Geier, L., Neiman, A. B. 2016; 93 (4): 042406


    We study the emergence and coherence of stochastic oscillations in star networks of excitable elements in which peripheral nodes receive independent random inputs. A biophysical model of a distal branch of sensory neuron in which peripheral nodes of Ranvier are coupled to a central node by myelinated cable segments is used along with a generic model of networked stochastic active rotators. We show that coherent oscillations can emerge due to stochastic synchronization of peripheral nodes and that the degree of coherence can be maximized by tuning the coupling strength and the size of the network. Analytical results are obtained for the strong-coupling regime of the active rotator network. In particular, we show that in the strong-coupling regime, the network dynamics can be described by an effective single active rotator with rescaled parameters and noise.

    View details for DOI 10.1103/PhysRevE.93.042406

    View details for Web of Science ID 000373586200007

    View details for PubMedID 27176328

  • Noise-controlled bistability in an excitable system with positive feedback EPL Kromer, J. A., Pinto, R. D., Lindner, B., Schimansky-Geier, L. 2014; 108 (2)
  • Event-triggered feedback in noise-driven phase oscillators PHYSICAL REVIEW E Kromer, J. A., Lindner, B., Schimansky-Geier, L. 2014; 89 (3): 032138


    Using a stochastic nonlinear phase oscillator model, we study the effect of event-triggered feedback on the statistics of interevent intervals. Events are associated with the entering of a new cycle. The feedback is modeled by an instantaneous increase (positive feedback) or decrease (negative feedback) of the oscillator frequency whenever an event occurs followed by an exponential decay on a slow time scale. In addition to the known excitable and oscillatory regimes, which are separated by a saddle node on invariant circle bifurcation, positive feedback can lead to bistable dynamics and a change of the system's excitability. The feedback has also a strong effect on noise-induced phenomena like coherence resonance or anticoherence resonance. Both positive and negative feedback can lead to more regular output for particular noise strengths. Finally, we investigate serial correlations in the sequence of interevent intervals that occur due to the additional slow dynamics. We derive approximations for the serial correlation coefficient and show that positive feedback results in extended positive interval correlations, whereas negative feedback yields short-ranging negative correlations. Investigating the interplay of feedback and the nonlinear phase dynamics close to the bifurcation, we find that correlations are most pronounced for optimal feedback strengths.

    View details for DOI 10.1103/PhysRevE.89.032138

    View details for Web of Science ID 000333702800004

    View details for PubMedID 24730820

  • Weighted-ensemble Brownian dynamics simulation: Sampling of rare events in nonequilibrium systems PHYSICAL REVIEW E Kromer, J. A., Schimansky-Geier, L., Toral, R. 2013; 87 (6): 063311


    We provide an algorithm based on weighted-ensemble (WE) methods, to accurately sample systems at steady state. Applying our method to different one- and two-dimensional models, we succeed in calculating steady-state probabilities of order 10(-300) and reproduce the Arrhenius law for rates of order 10(-280). Special attention is payed to the simulation of nonpotential systems where no detailed balance assumption exists. For this large class of stochastic systems, the stationary probability distribution density is often unknown and cannot be used as preknowledge during the simulation. We compare the algorithm's efficiency with standard Brownian dynamics simulations and the original WE method.

    View details for DOI 10.1103/PhysRevE.87.063311

    View details for Web of Science ID 000321096000012

    View details for PubMedID 23848810

  • Phason-induced dynamics of colloidal particles on quasicrystalline substrates EUROPEAN PHYSICAL JOURNAL E Kromer, J. A., Schmiedeberg, M., Roth, J., Stark, H. 2013; 36 (3): 25


    Phasons are special hydrodynamic modes that occur in quasicrystals. The trajectories of particles due to a phasonic drift were recently studied by Kromer et al. (Phys. Rev. Lett. 108, 218301 (2012)) for the case where the particles stay in the minima of a quasicrystalline potential. Here, we study the mean motion of colloidal particles in quasicrystalline laser fields when a phasonic drift or displacement is applied and also consider the cases where the colloids cannot follow the potential minima. While the mean square displacement is similar to the one of particles in a random potential with randomly changing potential wells, there also is a net drift of the colloids that reverses its direction when the phasonic drift velocity is increased. Furthermore, we explore the dynamics of the structural changes in a laser-induced quasicrystal during the rearrangement process that is caused by a steady phasonic drift or an instantaneous phasonic displacement.

    View details for DOI 10.1140/epje/i2013-13025-0

    View details for Web of Science ID 000317856000006

    View details for PubMedID 23512714

  • What Phasons Look Like: Particle Trajectories in a Quasicrystalline Potential PHYSICAL REVIEW LETTERS Kromer, J. A., Schmiedeberg, M., Roth, J., Stark, H. 2012; 108 (21): 218301


    Among the distinctive features of quasicrystals-structures with long-range order but without periodicity-are phasons. Phasons are hydrodynamic modes that, like phonons, do not cost free energy in the long-wavelength limit. For light-induced colloidal quasicrystals, we analyze the collective rearrangements of the colloids that occur when the phasonic displacement of the light field is changed. The colloidal model system is employed to study the link between the continuous description of phasonic modes in quasicrystals and collective phasonic flips of atoms. We introduce characteristic areas of reduced phononic and phasonic displacements and use them to predict individual colloidal trajectories. In principle, our method can be employed with all quasicrystalline systems in order to derive collective rearrangements of particles from the continuous description of phasons.

    View details for DOI 10.1103/PhysRevLett.108.218301

    View details for Web of Science ID 000304405000012

    View details for PubMedID 23003308