arXiv subjects

Jan Dvořák

Publications and source records attributed to Jan Dvořák.

10 recordsLinked to original sources

arXiv2026

On the measurability of Wigner time delays at shape resonances in photodetachment of polyatomic anions

The energy dependence of the complex phases of electron continuum wave functions carries information about electron dynamics. Streaking and attosecond interference experiments (called RABBIT) seek to measure this energy dependence, and therefore, the time delays of ionization. The long-range Coulomb interaction dominates in those experiments, and can obscure the low-energy features of the Wigner time delays that are the object of the measurement. Photodetachment of electrons from negative ions has no long-range Coulomb interaction, and RABBIT and streaking measurements of photodetachment delays have the potential to reveal time delays of up to one femtosecond in low-energy features. We predict the results of such experiments on a particularly interesting polyatomic example, the nitrate anion (NO$_3^-$), for both valence and core electron detachment. We simulate the experiments in these cases and analyze the underlying physics of measurements on polyatomic anions where many electron partial waves contribute and find that the angular dependence of the measured delays generally differs from the Wigner delays. However, we demonstrate that measurements performed for ejection directions close to the polarization of the light sources can directly access the Wigner delays that give a time-dependent window on electron-molecule interactions. A promising experiment involving core photodetachment of NO$_3^-$ with X-rays is proposed.

physics.atom-ph↗

arXiv2026

Effect of oxygen content on optical, structural, and dielectric properties of Al$_x$Ta$_y$O$_z$$ thin films

This study reports on the optical, structural, and dielectric properties of aluminum tantalum oxide (Al$_x$Ta$_y$O$_z$) thin films deposited at low temperature on silicon and steel substrates by pulsed direct current reactive magnetron sputtering of a target containing 80 at.% aluminum and 20 at.% tantalum in Ar/O$_2$ atmosphere. Oxygen flow rates ranging from 5.0 to 20 sccm corresponded to O content changes from 57.7 to 69.6 at.% and resulted in large differences in dielectric behavior, from films with no measurable dielectric strength to a dielectric strength of 231 V$μ$m$^{-1}$, respectively. Ab initio calculations were employed to explain the large property changes, and we show that a decrease in the dielectric strength can be linked to the formation of metal-metal bonds in the material, when the O content is less than what would correspond to a stoichiometric Ta$_2$O$_5$ and Al$_2$O$_3$ mixture. The electronic states corresponding to the metal--metal bonds are located in the band gap close to the top of the valence band, leading to an effective band gap reduction, which is directly supported by X-ray photoelectron spectroscopy valence band measurements and by a broad optical absorption in the visible region.

cond-mat.mtrl-sci↗

arXiv2025

Probing autoionization decay lifetimes of the $\mathbf{4d^{-1}6\boldsymbol{\ell}}$ core-excited states in xenon using attosecond noncollinear four-wave-mixing spectroscopy

The decay of core-excited states is a sensitive probe of autoionization dynamics and correlation effects in many-electron systems, occurring on the fastest timescales. Xenon, with its dense manifold of autoionizing resonances that can be coupled with near-infrared light, provides a platform to investigate these processes. In this work, the autoionization decay lifetimes of $4d^{-1}6\ell$ $(\ell = s, p, d, ...)$ core-excited states in xenon atoms are probed with extreme ultraviolet (XUV) attosecond noncollinear four-wave-mixing (FWM) spectroscopy. The $4d^{-1}_{\{5/2,\, 3/2\}}6p$ XUV-bright states (optically dipole allowed) exhibit decay lifetimes of $\sim$6 fs, which is consistent with spectator-type decay. In contrast, the $4d^{-1}_{\{5/2,\, 3/2\}}6s$ and $4d^{-1}_{\{5/2,\, 3/2\}}6d$ XUV-dark states (optically dipole forbidden) show longer decay lifetimes of $\sim$20 fs. Photoionization calculations confirm that all core-hole states with $4d$ character should decay via spectator channels in $\leq$ 6 fs, suggesting that the apparent longer dark state decay times arise from an alternative mechanism. A few-level simulation of the FWM process shows that the inclusion of a nearby, longer-lived dark state can mimic the experimental FWM signal, suggesting population cycling with a second electronic state with non-$4d$ character. Ab-initio calculations support the presence of such multi-electron excited states in the 60$-$70 eV range. These results demonstrate that FWM signals can encode coupled-state dynamics when probing complex systems, highlighting the importance of combining theoretical and experimental approaches to disentangle accurate core-level decay pathways and lifetimes.

physics.atom-ph↗

arXiv2024

Editing Mesh Sequences with Varying Connectivity

Time-varying connectivity of triangle mesh sequences leads to substantial difficulties in their processing. Unlike editing sequences with constant connectivity, editing sequences with varying connectivity requires addressing the problem of temporal correspondence between the frames of the sequence. We present a method for time-consistent editing of triangle mesh sequences with varying connectivity using sparse temporal correspondence, which can be obtained using existing methods. Our method includes a deformation model based on the usage of the sparse temporal correspondence, which is suitable for the temporal propagation of user-specified deformations of the edited surface with respect to the shape and true topology of the surface while preserving the individual connectivity of each frame. Since there is no other method capable of comparable types of editing on time-varying meshes, we compare our method and the proposed deformation model with a baseline approach and demonstrate the benefits of our framework.

cs.GR↗

arXiv2023

Vibronic dynamics in electron continuum -- iterative solvers

We present a general two-dimensional model of conical intersection between metastable states that are vibronically coupled not only directly but also indirectly through a virtual electron in the autodetachment continuum. This model is used as a test ground for design and comparison of iterative solvers for resonance dynamics in low-energy electron-molecule collisions. Two Krylov-subspace methods with various preconditioning schemes are compared. To demonstrate the applicability of the proposed methods on even larger models, we also test the performance of one of the methods on a recent model of vibrational excitation of CO$_2$ by electron impact based on three vibronically-coupled discrete states in continuum (Renner-Teller doublet of shape resonances coupled to sigma virtual state) including four vibrational degrees of freedom. Two-dimensional electron energy-loss spectra resulting from the electron-molecule scattering within the models are briefly discussed.

physics.chem-ph↗

arXiv2023

Current-induced bond rupture in single-molecule junctions: Effects of multiple electronic states and vibrational modes

Current-induced bond rupture is a fundamental process in nanoelectronic architectures such as molecular junctions and in scanning tunneling microscopy measurements of molecules at surfaces. The understanding of the underlying mechanisms is important for the design of molecular junctions that are stable at higher bias voltages and is a prerequisite for further developments in the field of current-induced chemistry. In this work, we analyse the mechanisms of current-induced bond rupture employing a recently developed method, which combines the hierarchical equations of motion approach in twin space with the matrix product state formalism, and allows accurate, fully quantum mechanical simulations of the complex bond rupture dynamics. Extending previous work [J. Chem. Phys. 154, 234702 (2021)], we consider specifically the effect of multiple electronic states and multiple vibrational modes. The results obtained for a series of models of increasing complexity show the importance of vibronic coupling between different electronic states of the charged molecule, which can enhance the dissociation rate at low bias voltages profoundly.

cond-mat.mes-hall↗

arXiv2020

Multi-Variant Time Constrained FlexRay Static Segment Scheduling

The FlexRay bus is a modern standard used in the automotive industry.It offers deterministic message transmission with zero jitter while using time-triggered scheduling in the static segment. When several vehicle variants (i.e. different models and their versions) share the same signal, the car manufacturers require to schedule such signal at the same time in all vehicle variants. This requirement simplifies the signal traceability and diagnostics in different vehicle variants using the same platform and simplifies reuse of components and tools. In this paper, we propose a first fit based heuristic algorithm which creates the schedules for several vehicle variants at once, while transmitting a given signal at the same time in all the schedules. The scheduling algorithm also takes the time constraints as release dates and deadlines into account. Finally, different algorithm versions are compared on benchmark sets and low computational time demands are validated on large instances.

eess.SY↗

arXiv2020

Makespan minimization of Time-Triggered traffic on a TTEthernet network

The reliability of the increasing number of modern applications and systems strongly depends on interconnecting technology. Complex systems which usually need to exchange, among other things, multimedia data together with safety-related information, as in the automotive or avionic industry, for example, make demands on both the high bandwidth and the deterministic behavior of the communication. TTEthernet is a protocol that has been developed to face these requirements while providing the generous bandwidth of Ethernet up to 1\,Gbit/s and enhancing its determinism by the Time-Triggered message transmission which follows the predetermined schedule. Therefore, synthesizing a good schedule which meets all the real-time requirements is essential for the performance of the whole system. In this paper, we study the concept of creating the communication schedules for the Time-Triggered traffic while minimizing its makespan. The aim is to maximize the uninterrupted gap for remaining traffic classes in each integration cycle. The provided scheduling algorithm, based on the Resource-Constrained Project Scheduling Problem formulation and the load balancing heuristic, obtains near-optimal (within 15\% of non-tight lower bound) solutions in 5 minutes even for industrial sized instances. The universality of the provided method allows easily modify or extend the problem statement according to particular industrial demands. Finally, the studied concept of makespan minimization is justified through the concept of scheduling with porosity according to the worst-case delay analysis of Event-Triggered traffic.

cs.NI↗

arXiv2019

Multi-Variant Scheduling of Critical Time-Triggered Communication in Incremental Development Process: Application to FlexRay

The portfolio of models offered by car manufacturing groups often includes many variants (i.e., different car models and their versions). With such diversity in car models, variant management becomes a formidable task. Thus, there is an effort to keep the variants as close as possible. This simple requirement forms a big challenge in the area of communication protocols. When several vehicle variants use the same signal, it is often required to simultaneously schedule such a signal in all vehicle variants. Furthermore, new vehicle variants are designed incrementally in such a way as to maintain backward compatibility with the older vehicles. Backward compatibility of time-triggered schedules reduces expenses relating to testing and fine-tuning of the components that interact with physical environment (e.g., electromagnetic compatibility issues). As this requirement provides for using the same platform, it simplifies signal traceability and diagnostics, across different vehicle variants, besides simplifying the reuse of components and tools. This paper proposes an efficient and robust heuristic algorithm, which creates the schedules for internal communication of new vehicle variants. The algorithm provides for variant management by ensuring compatibility among the new variants, besides preserving backward compatibility with the preceding vehicle variants. Based on the results of the proposed algorithm, the impact of maintaining compatibility among new variants and of preserving backward compatibility with the preceding variants on the scheduling procedure is examined and discussed. Thanks to the execution time of the algorithm, which is less than one second, the network parameters like the frame length and cycle duration are explored to find their best choice concerning the schedule feasibility.

eess.SY↗

arXiv2018

Using Two Independent Channels with Gateway for FlexRay Static Segment Scheduling

The FlexRay bus is a communication standard used in the automotive industry. It offers a deterministic message transmission in the static segment following a time-triggered schedule. Even if its bandwidth is ten times higher than the bandwidth of CAN, its throughput limits are going to be reached in high-class car models soon. A solution that could postpone this problem is to use an efficient scheduling algorithm that exploits both channels of the FlexRay. The significant and often neglected feature that can theoretically double the bandwidth is the possibility to use two independent communication channels that can intercommunicate through the gateway. In this paper, we propose a heuristic algorithm that decomposes the scheduling problem to the ECU-to-channel assignment subproblem which decides which channel the ECUs (Electronic Control Units) should be connected to and the channel scheduling subproblem which creates static segment communication schedules for both channels. The algorithm is able to create a schedule for cases where channels are configured in the independent mode as well as in the fault-tolerant mode or in cases where just part of the signals are fault-tolerant. Finally, the algorithm is evaluated on real data and synthesized data, and the relation between the portion of fault-tolerant signals and the number of allocated slots is presented.

eess.SY↗