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The interaction of light with the quantum-vacuum is predicted to give rise to some of the most fundamental and exotic processes in modern physics, which remain untested in the laboratory to date. Electron–positron pair production from a pure vacuum target, which has yet to be observed experimentally, is possibly the most iconic. The advent of ultra-intense lasers and laser accelerated GeV electron beams provide an ideal platform for the experimental realisation. Collisions of high energy γ-ray photons derived from the GeV electrons and intense laser fields result in detectable pair production rates at field strengths that approach and exceed the Schwinger limit in the centre-of-momentum frame. A detailed experiment has been designed to be implemented at the ATLAS laser at the centre of advanced laser applications. We show full calculations of the expected backgrounds and beam parameters which suggest that single pair events can be reliably generated and detected.

Photoproduction of electron-positron pairs by bremsstrahlung gamma-rays propagating through a high-intensity optical laser wave is studied. By calculating total pair production yields as well as energy and angular distributions of the produced particles for a range of laser intensities, we analyze the influence that the broad frequency spectrum of bremsstrahlung exerts on the properties of the process in the transition region between the perturbative and non-perturbative interaction regimes. In particular, we demonstrate a continuous shifting of the mainly contributing interval of bremsstrahlung frequencies during the course of the transition and indicate characteristic signatures of the laser-dressed particle mass.

Relativistic strong-field ionization of hydrogen-like atoms or ions in a constant crossed electromagnetic field is studied. The transition amplitude is formulated within the strong-field approximation in G\"oppert-Mayer gauge, with initial and final electron states being described by the corresponding Dirac-Coulomb and Dirac-Volkov wave functions, respectively. Coulomb corrections to the electron motion during tunneling are taken into account by adjusting an established method to the present situation. Total and energy-differential ionization rates are calculated and compared with predictions from other theories in a wide range of atomic numbers and applied field strengths.

The Millikan Oil Drop Experiment is frequently encountered in historical surveys of atomic theory presented during general chemistry courses, but is often not well understood by freshmen. As an aid to understanding, an analogy is drawn between the manner in which the charge on a single electron is deduced from the total charge on an oil drop, and a rather peculiar pricing system in a surreal candy store.

Double ionization of an atom by single-photon absorption in the presence of a neighbouring atom is studied. The latter is, first, resonantly photoexcited and, afterwards, transfers the excitation energy radiationlessly to the other atom, leading to its double ionization. The process relies on the combined effect of interatomic and intraatomic electron correlations. It can dominate over the direct double photoionization by several orders of magnitude at interatomic distances up to few nanometers. The relative position of the neighbouring atom is shown to exert a characteristic influence on the angular distribution of emitted electrons.

Near-future experiments intend to detect strong-field Breit-Wheeler pair creation from the collision between bremsstrahlung bursts containing GeV-\\(\\gamma\\) quanta and high-intensity laser pulses. In this theoretical study, we investigate the influence of laser focusing, radiation reaction and a broad bremsstrahlung \\(\\gamma\\) spectrum on the energy and angular distributions of created pairs. Understanding the role of these inherent reaction attributes provides relevant insights for experimental detection strategies and data interpretation. We show that the inclusion of radiation reaction leads to a narrow energy spectrum of the yielded particles, whose maximum is shifted to substantially lower energies as compared to the case in which radiative energy losses are ignored. The broad bremsstrahlung spectrum also has distinct influence on the particle distributions, whereas the impact of laser focusing turns out to be rather moderate in the considered parameter regime.

Electron scattering and dielectronic recombination with an ion in the presence of a neighboring atom is studied. The incident electron is assumed to be captured by the ion, leading to resonant excitation of the atom which afterwards may stabilize either by electron re-emission or radiative decay. We show that the participation of the atom can strongly affect, both quantitatively and qualitatively, the corresponding processes of electron scattering and recombination. Various ion-atom systems and electronic transitions are considered. In particular we show that electron scattering under backward angles may be strongly enhanced and derive the scaling behavior of two-center dielectronic recombination with the principal quantum numbers of the participating atomic states.

PurposeThe COVID-19 pandemic has hit different industries and firms with widely differing degrees of severity. The authors investigate whether ownership structure (family vs non-family) might represent a differentiating factor. The article's purpose is to conduct an initial, descriptive analysis of the impact of COVID-19 on different stock and operating performance measures of listed German companies.Design/methodology/approachThe authors use a sample of 299 listed companies in Germany and gathered operating as well as stock market performance data following the outbreak of COVID-19. For the purpose of this paper, the authors solely focus on static and descriptive observations thus far. The intention of this paper is to describe potential implications for more differentiated, especially multivariate causal research, on family businesses in a post-COVID world.FindingsThe results indicate that, over the last five years, stock returns of family businesses have been higher than those of non-family firms. This effect seems to have been more pronounced during the first month following the COVID-19 outbreak. When applying operating measures, the outperformance becomes even more evident. The findings therefore seem to support the hypothesis proffered in the literature that family involvement enhances the potential for resilience in such firms.Originality/valueScholars on COVID-19 crisis performance have begun to explore firm-level factors related to financial and organizational factors, industry characteristics and country-level factors. The research extends this line of inquiry by probing the importance of family involvement in ownership.

Flexible electronics have gained popularity because of their capability to combine softness and functionality. Soft resistive sensors are susceptible to mechanical stimuli and detecting temperature selectively remains a challenge. In this study, soft flexible thermistors are developed for detecting temperature changes based on the positive temperature coefficient (PTC) effect, selectively. By thermomechanical analysis and differential scanning calorimetry, it is observed that thermoplastic elastomers with higher thermal expansion and semicrystalline morphology result in a sensitive thermistor response. To achieve a high sensitivity in temperature and low sensitivity in the detection of mechanical stimulus, a low‐carbon filler content is required. The opposite trend is seen for the piezoresistive sensors for mechanical strain detection. Both sensory material types are compatible with thermoplastic material extrusion‐based additive manufacturing. The method is used for the fabrication of the sensing elements and an open‐source prosthetic hand. The strain sensor detects the bending of the fingers and the temperature sensor detects the temperature when in contact with a heated surface, successfully. In addition, the temperature sensor is used as a tactile sensor to detect contact with a non‐heated surface. Combining selective multisensory capabilities will significantly affect the future development of sensorized prosthetic devices and wearable electronics. A sensorized prosthetic hand is presented with integrated temperature, tactile, and proprioceptive sensing. For achieving a selective response, the composite filler content, thermal expansion, and crystallinity of the matrix are tuned accordingly. Thanks to the flexible sensing, the prosthetic hand can recognize the temperature of the contact surface and position of the fingers, mimicking the senses of the human hand.

Epstein-Barr-Virus (EBV) plays an important role as trigger or cofactor for various autoimmune diseases. In a subset of patients with Chronic Fatigue Syndrome (CFS) disease starts with infectious mononucleosis as late primary EBV-infection, whereby altered levels of EBV-specific antibodies can be observed in another subset of patients. We performed a comprehensive mapping of the IgG response against EBV comparing 50 healthy controls with 92 CFS patients using a microarray platform. Patients with multiple sclerosis (MS), systemic lupus erythematosus (SLE) and cancer-related fatigue served as controls. 3054 overlapping peptides were synthesised as 15-mers from 14 different EBV proteins. Array data was validated by ELISA for selected peptides. Prevalence of EBV serotypes was determined by qPCR from throat washing samples. EBV type 1 infections were found in patients and controls. EBV seroarray profiles between healthy controls and CFS were less divergent than that observed for MS or SLE. We found significantly enhanced IgG responses to several EBNA-6 peptides containing a repeat sequence in CFS patients compared to controls. EBNA-6 peptide IgG responses correlated well with EBNA-6 protein responses. The EBNA-6 repeat region showed sequence homologies to various human proteins. Patients with CFS had a quite similar EBV IgG antibody response pattern as healthy controls. Enhanced IgG reactivity against an EBNA-6 repeat sequence and against EBNA-6 protein is found in CFS patients. Homologous sequences of various human proteins with this EBNA-6 repeat sequence might be potential targets for antigenic mimicry.