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We identify the background driving distribution functions (BDDF) for self-decomposable distributions (random variables). For log-gamma variables and their background driving variables, we find their series representations. An innovation variable for Bessel-K distribution is given as a compound Poisson variable. [ABSTRACT FROM AUTHOR]

In this review we discuss various simulation methods for modeling nanoplasmas created from finite-size samples after their irradiation with femtosecond, intense X-ray pulses. Depending on the sample composition and its size, either a particle method or a transport method can be applied. Also, the observables of interest influence the choice of the simulation method. The current status of dedicated methods developed by the CFEL Theory Division at DESY in Hamburg and their possible extensions are presented together with some application examples. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

SUMMARY Recently, the passivity results for linear time-invariant systems were successfully extended to nonlinear and nonstationary systems, thus guaranteeing stability of adaptive control of nonlinear square systems. Based on this theoretical development, this paper presents the development of a new class of direct adaptive controllers, which employ a new decentralized adaptation law mechanism that is developed from the simple adaptive control technique. The resulting direct adaptive control methodology is referred to as decentralized simple adaptive control. A simplification of this new control algorithm, referred to as decentralized modified simple adaptive control, is also presented. In addition, it is shown that both control methodologies can be modified to avoid divergence in practical situations, where the trajectory tracking errors cannot reach zero. Using Lyapunov direct method and Lasalle's invariance principle for nonautonomous systems, the formal proof of stability is established. As well, a numerical simulation study for a trajectory tracking problem by a rigid-joint manipulator is presented to illustrate the new adaptive control approaches. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The optimal performance of the Kalman filters is highly dependent on the measurement and process noise characteristics, making the whole system unable to achieve the desired estimation in the presence of non-Gaussian mean noise distribution and high initial uncertainties. Recently, the H-infinity filter, as a robust algorithm, has been broadly used, as it is not being dependent on the pre-knowledge of the noise nature; however, making a balance between high robustness and estimation accuracy is a challenging issue. Hence, to overcome this problem, a new adaptive H-infinity extended Kalman filter (AHEKF) was designed in this paper, which benefits from both high robustness and precision. The suggested algorithm contains two adaptive sections to achieve high accuracy as well as controlling the effects of time-varying noise characteristics, high initial uncertainties, and abnormal data that can degrade the accuracy of state estimation in an integrated navigation system. The presented algorithm was used to integrate data from two independent sensors data. The simulation results for an inertial navigation system (INS)/global positioning system (GPS) sensor fusion are presented and compared with the standard H-infinity filter, extended Kalman filter (EKF), and unscented Kalman filter (UKF) to show the effectiveness of the proposed algorithm. Evaluations demonstrate that the AHEKF achieves over 50% higher accuracy and robustness, and over 2.5 times faster convergence of estimation errors than the standard H-infinity filter. [ABSTRACT FROM AUTHOR]

The classes of selfdecomposable and s-selfdecomposable probability measures are known to have representations as the distributions of random integrals. In this paper we provide such random integral representations for the class of generalized s-selfdecomposable and the class of selfdecomposable distributions that have the so-called factorization property. [ABSTRACT FROM AUTHOR]

The behavior of small samples in very short and intense hard X-ray pulses is studied by molecular dynamics type calculations. The main emphasis is put on the effect of various tamper layers about the sample. This is discussed from the point of view of structural imaging of single particles, including not only the distortion of the structure but also the background conditions. A detailed picture is given about the Coulomb explosion, with explanation of the tampering mechanism. It is shown that a thin water layer is efficient in slowing down the distortion of the atomic structure, but it gives a significant contribution to the background. [ABSTRACT FROM AUTHOR]

Abstract: Among the future X-ray sources linac-based X-ray free electron lasers are close to realization. They will produce extremely short (<100fs) and intense hard X-ray pulses (∼1012 photon/pulse). The unique features of this beam will allow the study of the atomic structure and the different physical and chemical processes in solids at a level which is not accessible today. However, to understand the experimental results a detailed picture of what happens during the burst in the sample is necessary. In several suggested applications, small samples containing only 103–106 atoms are the possible candidates. In order to have an understanding about the atomic motions, we performed model calculations on the dynamics of particles of a cluster in an intense hard X-ray pulse. The movement of the particles was followed by non-relativistic classical dynamics. The main processes: photo-absorption, Auger process, inelastic and elastic scattering of electrons were taken into account by their respective cross sections. Here, we report our findings on clusters containing various elements. The results show that the clusters disintegrate via Coulomb explosion, similar to small clusters in intense laser beam. However, the dynamics of the explosion is significantly different. We investigate the effect of cluster size, pulse length, atom density and composition on the explosion. We discuss the consequences of our results to single-molecule imaging by the free-electron laser pulses, recently proposed by Neutze et al. [R. Neutze, R. Wouts, D. Spoel, E. Weckert, J. Hajdu, Nature, 406 (2000) 752]. The critical evaluation of these results gives guidelines and sets important limits on experimental conditions for future experiments aiming for single-molecule structure solution. [Copyright &y& Elsevier]

Operational problems with robot manipulators in space relate to several factors, most importantly, structural flexibility and subsequent difficulties with their position control. In this paper we present control methods for endpoint tracking of a 12.6 x 12.6 m² trajectory by a two-link robot manipulator. Initially, a manipulator with rigid links is modeled using inverse dynamics, a linear quadratic regulator and fuzzy logic schemes actuated by a Jacobian transpose control law computed using dominant cantilever and pinned-pinned assumed mode frequencies. The inverse dynamics model is pursued further to study a manipulator with flexible links where nonlinear rigid-link dynamics are coupled with dominant assumed modes for cantilever and pinned-pinned beams. A time delay in the feedback control loop represents elastic wave travel time along the links to generate non-minimum phase response. A time delay acting on control commands ameliorates non-minimum phase response. Finally, a fuzzy logic system outputs a variable to adapt the control law in response to elastic deformation inputs. Results show greater endpoint position control accuracy using a flexible inverse dynamics robot model combined with a fuzzy logic adapted control law and time delays than could be obtained for the rigid dynamics models. [ABSTRACT FROM AUTHOR]

In this paper we examine the behavior of small cluster of atoms in a short (10-50 fs) very intense hard X-ray (10 keV) pulse. We use numerical modeling based on the non-relativistic classical equation of motion. Quantum processes are taken into account by the respective cross-sections. We show that there is a Coulomb explosion, which has a different dynamics than one finds in classical laser driven cluster explosions. We discuss the consequences of our results to single molecule imaging by the free electron laser pulses. [ABSTRACT FROM AUTHOR]

Using electron spectroscopy, we have investigated nanoplasma formation from noble gas clusters exposed to high-intensity hard-x-ray pulses at ~5 keV. Our experiment was carried out at the SPring-8 Angstrom Compact free electron LAser (SACLA) facility in Japan. Dedicated theoretical simulations were performed with the molecular dynamics tool XMDYN. We found that in this unprecedented wavelength regime nanoplasma formation is a highly indirect process. In the argon clusters investigated, nanoplasma is mainly formed through secondary electron cascading initiated by slow Auger electrons. Energy is distributed within the sample entirely through Auger processes and secondary electron cascading following photoabsorption, as in the hard x-ray regime there is no direct energy transfer from the field to the plasma. This plasma formation mechanism is specific to the hard-x-ray regime and may, thus, also be important for XFEL-based molecular imaging studies. In xenon clusters, photo- and Auger electrons contribute more significantly to the nanoplasma formation. Good agreement between experiment and simulations validates our modelling approach. This has wide-ranging implications for our ability to quantitatively predict the behavior of complex molecular systems irradiated by high-intensity hard x-rays. [ABSTRACT FROM AUTHOR]

Classical molecular dynamics (MD) has been successfully applied to model radiation-induced dynamics of highly ionized assemblies of atoms, including the dynamics of electrons, released during ionization processes. Here we test the applicability of a classical MD scheme in a yet unexplored regime: for a strongly bound molecular system represented by buckminsterfullerene, C60, singly ionized by an x-ray pulse. We show MD simulation results obtained for electron and ion spectra, and compare them to existing experimental data from synchrotron experiments. We identify the sources of discrepancies between the classical simulations and experiments, and discuss possible improvements of the model. Our calculations establish limits for the applicability of classical MD simulations to x-ray irradiated systems. These classical simulations are much more computationally efficient than any rigorous quantum calculations, and are, therefore, often the only option. The conclusions obtained can be useful for planning computational studies of irradiated large molecular assemblies. [ABSTRACT FROM AUTHOR]

In the last 15 years, several techniques based on the holographic principle have been developed for the study of the 3D local order in solids. These methods use various particles: electrons, hard X-ray photons, gamma photons, or neutrons to image the atoms. Although the practical realisation of the various imaging experiments is very different, there is a common thread; the use of inside reference points for holographic imaging. In this paper, we outline the basics of atomic resolution holography using inside reference points, with particular emphasis on the hard X-ray case. Furthermore, we outline the experimental requirements and what has been practically realized in the last decade. Lastly, we give examples of applications and future perspectives. [Copyright &y& Elsevier]

Imaging of the structure of single proteins or other biomolecules with atomic resolution would be enormously beneficial to structural biology. X-ray free-electron lasers generate highly intense and ultrashort x-ray pulses, providing a route towards imaging of single molecules with atomic resolution. The information on molecular structure is encoded in the coherent x-ray scattering signal. In contrast to crystallography there are no Bragg reflections in single molecule imaging, which means the coherent scattering is not enhanced. Consequently, a background signal from incoherent scattering deteriorates the quality of the coherent scattering signal. This background signal cannot be easily eliminated because the spectrum of incoherently scattered photons cannot be resolved by usual scattering detectors. We present an ab initio study of incoherent x-ray scattering from individual carbon atoms, including the electronic radiation damage caused by a highly intense x-ray pulse. We find that the coherent scattering pattern suffers from a significant incoherent background signal at high resolution. For high x-ray fluence the background signal becomes even dominating. Finally, based on the atomic scattering patterns, we present an estimation for the average photon count in single molecule imaging at high resolution. By varying the photon energy from 3.5 keV to 15 keV, we find that imaging at higher photon energies may improve the coherent scattering signal quality. [ABSTRACT FROM AUTHOR]

During the coherent diffraction imaging (CDI) of a single object with an intense x-ray free-electron laser (FEL) pulse, the structure of the object changes due to the progressing radiation damage. Electrons are released from atoms and ions during photo-, Auger- and collisional ionization processes. More and more ions appear in the sample. The repulsive force between ions makes them move apart. Form factors of the created ions are reduced when compared with the atomic form factors. Additional scattering of energetic photons from the free electrons confined within the beam focus deteriorates the obtained diffractive signal. Here, we consider pulses short enough to neglect ionic movement and investigate how (i) the decrease of atomic form factors due to the progressing ionization of the sample and (ii) the scattering from the free electrons influence the signal obtained during the CDI. We quantify the loss of structural information about the object due to these effects with hydrodynamic simulations. Our study has implications for the experiments planned on high-resolution three-dimensional imaging of single reproducible particles with x-ray FELs. [ABSTRACT FROM AUTHOR]