Sensitivity of nonlinear photoionization to resonance substructure in collective excitation

Collective behaviour is a characteristic feature in many-body systems, important for developments in fields such as magnetism, superconductivity, photonics and electronics. Recently, there has been increasing interest in the optically nonlinear response of collective excitations. Here we demonstrate how the nonlinear interaction of a many-body system with intense XUV radiation can be used as an effective probe for characterizing otherwise unresolved features of its collective response. Resonant photoionization of atomic xenon was chosen as a case study. The excellent agreement between experiment and theory strongly supports the prediction that two distinct poles underlie the giant dipole resonance. Our results pave the way towards a deeper understanding of collective behaviour in atoms, molecules and solid-state systems using nonlinear spectroscopic techniques enabled by modern short-wavelength light sources

Two-electron processes in multiple ionization under strong soft-x-ray radiation

In a combined experimental and theoretical study we have investigated the ionization of atomic argon upon irradiation with intense soft-x-ray pulses of 105 eV photon energy from the free-electron laser FLASH. The measured ion yields show charge states up to Ar7+. The comparison with the theoretical study of the underlying photoionization dynamics highlights the importance of excited states in general and of processes governed by electron correlation in particular, namely, ionization with excitation and shake-off, processes usually inaccessible by measurements of ionic yields only. The Ar7+ yield shows a clear deviation from the predictions of the commonly used model of sequential ionization via single-electron processes and the observed signal can only be explained by taking into account the full multiplet structure of the involved configurations and by inclusion of two-electron processes. The competing process of two-photon ionization from the ground state of Ar6+ is calculated to be orders of magnitude smaller

Axonal transport proteins and depressive like behavior, following Chronic Unpredictable Mild Stress in male rat

Background: A common mood disorder, depression has long been considered a leading cause of disability worldwide. Chronic stress is involved in the development of various psychiatric diseases including major depressive disorder. Stress can induce depressive-like symptoms and initiate neurodegenerative processes in the brain. The neurodegenerative theory of depression holds impaired axonal transport as a negative factor in neural survival. Axonal transport is a critical mechanism for normal neuronal function, playing crucial roles in axon growth, neurotransmitter secretion, normal mitochondrial function and neural survival. Methods and materials: To investigate the effects of stress-induced depression, in the present study, we evaluated behavior by forced swimming test (FST), corticosterone plasma level by ELISA assay, hippocampal mRNA expression of three genes (NGF, kinesin and dynein) via real-time PCR and hippocamp count by Nissl staining in male Wistar rats. Results: Our data demonstrated a significant decrease in the expression of NGF, kinesin and dynein genes in CUMS groups compared to the control group (non-stressed) (p < 0.05). CUMS also caused an elevation in immobility time and corticosterone plasma level in the stressed group compared to the controls (p < 0.01 and p < 0.05, respectively). Conclusion: The results suggested that the possibility of stress-induced depressive behavior associated with hippocampal neurodegeneration process is correlated with a low expression of kinesin and dynein, the two most important proteins in axonal transport. © 2018 Elsevier Inc

Axonal transport proteins and depressive like behavior, following Chronic Unpredictable Mild Stress in male rat

Background: A common mood disorder, depression has long been considered a leading cause of disability worldwide. Chronic stress is involved in the development of various psychiatric diseases including major depressive disorder. Stress can induce depressive-like symptoms and initiate neurodegenerative processes in the brain. The neurodegenerative theory of depression holds impaired axonal transport as a negative factor in neural survival. Axonal transport is a critical mechanism for normal neuronal function, playing crucial roles in axon growth, neurotransmitter secretion, normal mitochondrial function and neural survival. Methods and materials: To investigate the effects of stress-induced depression, in the present study, we evaluated behavior by forced swimming test (FST), corticosterone plasma level by ELISA assay, hippocampal mRNA expression of three genes (NGF, kinesin and dynein) via real-time PCR and hippocamp count by Nissl staining in male Wistar rats. Results: Our data demonstrated a significant decrease in the expression of NGF, kinesin and dynein genes in CUMS groups compared to the control group (non-stressed) (p < 0.05). CUMS also caused an elevation in immobility time and corticosterone plasma level in the stressed group compared to the controls (p < 0.01 and p < 0.05, respectively). Conclusion: The results suggested that the possibility of stress-induced depressive behavior associated with hippocampal neurodegeneration process is correlated with a low expression of kinesin and dynein, the two most important proteins in axonal transport. © 2018 Elsevier Inc

Time zero determination for FEL pump-probe studies based on ultrafast melting of bismuth

A common challenge for pump-probe studies of structural dynamics at X-ray free-electron lasers (XFELs) is the determination of time zero (T0)—the time an optical pulse (e.g., an optical laser) arrives coincidently with the probe pulse (e.g., a XFEL pulse) at the sample position. In some cases, T0 might be extracted from the structural dynamics of the sample's observed response itself, but generally, an independent robust method is required or would be superior to the inferred determination of T0. In this paper, we present how the structural dynamics in ultrafast melting of bismuth can be exploited for a quickly performed, reliable and accurate determination of T0 with a precision below 20 fs and an overall experimental accuracy of 50 fs to 150 fs (estimated). Our approach is potentially useful and applicable for fixed-target XFEL experiments, such as serial femtosecond crystallography, utilizing an optical pump pulse in the ultraviolet to near infrared spectral range and a pixelated 2D photon detector for recording crystallographic diffraction patterns in transmission geometry. In comparison to many other suitable approaches, our method is fairly independent of the pumping wavelength (UV–IR) as well as of the X-ray energy and offers a favorable signal contrast. The technique is exploitable not only for the determination of temporal characteristics of the experiment at the interaction point but also for investigating important conditions affecting experimental control such as spatial overlap and beam spot sizes