TY - JOUR A1 - Yochelis, Arik A1 - Flemming, Sven A1 - Beta, Carsten T1 - Versatile patterns in the actin cortex of motile cells BT - self-organized pulses can coexist with macropinocytic ring-shaped waves JF - Physical review letters N2 - Self-organized patterns in the actin cytoskeleton are essential for eukaryotic cellular life. They are the building blocks of many functional structures that often operate simultaneously to facilitate, for example, nutrient uptake and movement of cells. However, identifying how qualitatively distinct actin patterns can coexist remains a challenge. Using bifurcation theory of a mass conserved activator-inhibitor system, we uncover a generic mechanism of how different actin waves-traveling waves and excitable pulses- organize and simultaneously emerge. Live-cell imaging experiments indeed reveal that narrow, planar, and fast-moving excitable pulses may coexist with ring-shaped macropinocytic actin waves in the cortex of motile amoeboid cells. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevLett.129.088101 SN - 0031-9007 SN - 1079-7114 VL - 129 IS - 8 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Yochelis, Arik A1 - Beta, Carsten A1 - Gov, Nir S. T1 - Excitable solitons BT - annihilation, crossover, and nucleation of pulses in mass-conserving activator-inhibitor media JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Excitable pulses are among the most widespread dynamical patterns that occur in many different systems, ranging from biological cells to chemical reactions and ecological populations. Traditionally, the mutual annihilation of two colliding pulses is regarded as their prototypical signature. Here we show that colliding excitable pulses may exhibit solitonlike crossover and pulse nucleation if the system obeys a mass conservation constraint. In contrast to previous observations in systems without mass conservation, these alternative collision scenarios are robustly observed over a wide range of parameters. We demonstrate our findings using a model of intracellular actin waves since, on time scales of wave propagations over the cell scale, cells obey conservation of actin monomers. The results provide a key concept to understand the ubiquitous occurrence of actin waves in cells, suggesting why they are so common, and why their dynamics is robust and long-lived. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevE.101.022213 SN - 2470-0045 SN - 2470-0053 VL - 101 IS - 2 PB - American Physical Society CY - Melville, NY ER - TY - JOUR A1 - Yin, Zhong A1 - Rajkovic, Ivan A1 - Veedu, Sreevidya Thekku A1 - Deinert, Sascha A1 - Raiser, Dirk A1 - Jain, Rohit A1 - Fukuzawa, Hironobu A1 - Wada, Shin-ichi A1 - Quevedo, Wilson A1 - Kennedy, Brian A1 - Schreck, Simon A1 - Pietzsch, Annette A1 - Wernet, Philippe A1 - Ueda, Kyoshi A1 - Föhlisch, Alexander A1 - Techert, Simone T1 - Ionic solutions probed by resonant inelastic X-ray scattering JF - Zeitschrift für physikalische Chemie : international journal of research in physical chemistry and chemical physics N2 - X-ray spectroscopy is a powerful tool to study the local charge distribution of chemical systems. Together with the liquid jet it becomes possible to probe chemical systems in their natural environment, the liquid phase. In this work, we present X-ray absorption (XA), X-ray emission (XE) and resonant inelastic X-ray scattering (RIXS) data of pure water and various salt solutions and show the possibilities these methods offer to elucidate the nature of ion-water interaction. KW - X-ray Spectroscopy KW - XAS KW - XES KW - RIXS KW - Anions KW - Cations KW - Liquid Jet KW - Synchrotron Radiation Y1 - 2015 U6 - https://doi.org/10.1515/zpch-2015-0610 SN - 0942-9352 VL - 229 IS - 10-12 SP - 1855 EP - 1867 PB - De Gruyter CY - Berlin ER - TY - JOUR A1 - Yin, Zhong A1 - Rajkovic, Ivan A1 - Kubicek, Katharina A1 - Quevedo, Wilson A1 - Pietzsch, Annette A1 - Wernet, Philippe A1 - Föhlisch, Alexander A1 - Techert, Simone T1 - Probing the Hofmeister effect with ultrafast core-hole spectroscopy JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - In the current work, X-ray emission spectra of aqueous solutions of different inorganic salts within the Hofmeister series are presented. The results reflect the direct interaction of the ions with the water molecules and therefore, reveal general properties of the salt-water interactions. Within the experimental precision a significant effect of the ions on the water structure has been observed but no ordering according to the structure maker/structure breaker concept could be mirrored in the results indicating that the Hofmeister effect if existent may be caused by more complex interactions. Y1 - 2014 U6 - https://doi.org/10.1021/jp504577a SN - 1520-6106 VL - 118 IS - 31 SP - 9398 EP - 9403 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Yin, Zhong A1 - Inhester, Ludger A1 - Veedu, Sreevidya Thekku A1 - Quevedo, Wilson A1 - Pietzsch, Annette A1 - Wernet, Philippe A1 - Groenhof, Gerrit A1 - Föhlisch, Alexander A1 - Grubmueller, Helmut A1 - Techert, Simone T1 - Cationic and Anionic Impact on the Electronic Structure of Liquid Water JF - The journal of physical chemistry letters N2 - Hydration shells around ions are crucial for many fundamental biological and chemical processes. Their local physicochemical properties are quite different from those of bulk water and hard to probe experimentally. We address this problem by combining soft X-ray spectroscopy using a liquid jet and molecular dynamics (MD) simulations together with ab initio electronic structure calculations to elucidate the water ion interaction in a MgCl2 solution at the molecular level. Our results reveal that salt ions mainly affect the electronic properties of water molecules in close vicinity and that the oxygen K-edge X-ray emission spectrum of water molecules in the first solvation shell differs significantly from that of bulk water. Ion-specific effects are identified by fingerprint features in the water X-ray emission spectra. While Mg2+ ions cause a bathochromic shift of the water lone pair orbital, the 3p orbital of the Cl- ions causes an additional peak in the water emission spectrum at around 528 eV. Y1 - 2017 U6 - https://doi.org/10.1021/acs.jpclett.7b01392 SN - 1948-7185 VL - 8 SP - 3759 EP - 3764 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Yilmaz, Sükrü A1 - Wirges, Werner A1 - Bauer-Gogonea, Simona A1 - Bauer, Siegfried A1 - Gerhard, Reimund A1 - Michelotti, F. A1 - Toussaere, E. A1 - Levenson, R. A1 - Liang, J. A1 - Zyss, Joseph T1 - Dielectric, pyroelectric and electro-optic monitoring of the cross-linking process and photo-induced poling of Red Acid Magly Y1 - 1997 ER - TY - JOUR A1 - Yeste, Maria Pilar A1 - Primus, Philipp-Alexander A1 - Alcantara, Rodrigo A1 - Cauqui, Miguel Angel A1 - Calvino, Juan Jose A1 - Pintado, José María A1 - Blanco, Ginesa T1 - Surface characterization of two Ce0.62Zr0.38O2 mixed oxides with different reducibility JF - Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces N2 - This paper presents a study of the surface properties of two Ce/Zr mixed oxides with different reducibility, obtained by applying distinct thermal ageing treatments to an oxide with the composition Ce0.62Zr0.38O2. The surface composition was investigated by XPS. Chemical reactivity of the surface was studied by adsorption of the probe molecules CO2, D-2 and methanol. Nanostructural characterization was carried out by XRD, Raman and high-resolution Eu3+ spectroscopy (FLNS). The characterization showed only slight variations in surface composition and bulk Ce-Zr distribution, but hardy differences concerning the type and strength of acidic surface centres, as well as strong differences in the ability to dissociate hydrogen. Structural variations between both samples were identified by comparing the optical spectra of Eu3+ in surface doped samples. KW - Ce/Zr KW - Surface properties KW - Reactive adsorption KW - Hydrogen activation Y1 - 2020 U6 - https://doi.org/10.1016/j.apsusc.2019.144255 SN - 0169-4332 SN - 1873-5584 VL - 503 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Yeldesbay, Azamat A1 - Pikovskij, Arkadij A1 - Rosenblum, Michael T1 - Chimeralike states in an ensemble of globally coupled oscillators JF - Physical review letters N2 - We demonstrate the emergence of a complex state in a homogeneous ensemble of globally coupled identical oscillators, reminiscent of chimera states in nonlocally coupled oscillator lattices. In this regime some part of the ensemble forms a regularly evolving cluster, while all other units irregularly oscillate and remain asynchronous. We argue that the chimera emerges because of effective bistability, which dynamically appears in the originally monostable system due to internal delayed feedback in individual units. Additionally, we present two examples of chimeras in bistable systems with frequency-dependent phase shift in the global coupling. Y1 - 2014 U6 - https://doi.org/10.1103/PhysRevLett.112.144103 SN - 0031-9007 SN - 1079-7114 VL - 112 IS - 14 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Ye, Shengyi A1 - Kurth, William S. A1 - Hospodarsky, George B. A1 - Persoon, Ann M. A1 - Sulaiman, Ali H. A1 - Gurnett, Don A. A1 - Morooka, Michiko A1 - Wahlund, Jan-Erik A1 - Hsu, Hsiang-Wen A1 - Sternovsky, Zoltan A1 - Wang, Xu A1 - Horanyi, M. A1 - Seiss, Martin A1 - Srama, Ralf T1 - Dust Observations by the Radio and Plasma Wave Science Instrument During JF - Geophysical research letters N2 - Plain Language Summary Cassini flew through the gap between Saturn and its rings for 22 times before plunging into the atmosphere of Saturn, ending its 20-year mission. The radio and plasma waves instrument on board Cassini helped quantify the dust hazard in this previously unexplored region. The measured density of large dust particles was much lower than expected, allowing high-value science observations during the subsequent Grand Finale orbits. Y1 - 2018 U6 - https://doi.org/10.1029/2018GL078059 SN - 0094-8276 SN - 1944-8007 VL - 45 IS - 19 SP - 10101 EP - 10109 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Ye, S. -Y. A1 - Kurth, William S. A1 - Hospodarsky, George B. A1 - Persoon, Ann M. A1 - Gurnett, Don A. A1 - Morooka, Michiko A1 - Wahlund, Jan-Erik A1 - Hsu, Hsiang-Wen A1 - Seiss, Martin A1 - Srama, Ralf T1 - Cassini RPWS dust observation near the Janus/Epimetheus orbit JF - Journal of geophysical research : Space physics N2 - During the Ring Grazing orbits near the end of Cassini mission, the spacecraft crossed the equatorial plane near the orbit of Janus/Epimetheus (similar to 2.5 Rs). This region is populated with dust particles that can be detected by the Radio and Plasma Wave Science (RPWS) instrument via an electric field antenna signal. Analysis of the voltage waveforms recorded on the RPWS antennas provides estimations of the density and size distribution of the dust particles. Measured RPWS profiles, fitted with Lorentzian functions, are shown to be mostly consistent with the Cosmic Dust Analyzer, the dedicated dust instrument on board Cassini. The thickness of the dusty ring varies between 600 and 1,000 km. The peak location shifts north and south within 100 km of the ring plane, likely a function of the precession phase of Janus orbit. KW - Saturn KW - dust KW - ring Y1 - 2018 U6 - https://doi.org/10.1029/2017JA025112 SN - 2169-9380 SN - 2169-9402 VL - 123 IS - 6 SP - 4952 EP - 4960 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Ye, Fangyuan A1 - Zhang, Shuo A1 - Warby, Jonathan A1 - Wu, Jiawei A1 - Gutierrez-Partida, Emilio A1 - Lang, Felix A1 - Shah, Sahil A1 - Saglamkaya, Elifnaz A1 - Sun, Bowen A1 - Zu, Fengshuo A1 - Shoai, Safa A1 - Wang, Haifeng A1 - Stiller, Burkhard A1 - Neher, Dieter A1 - Zhu, Wei-Hong A1 - Stolterfoht, Martin A1 - Wu, Yongzhen T1 - Overcoming C₆₀-induced interfacial recombination in inverted perovskite solar cells by electron-transporting carborane JF - Nature Communications N2 - Inverted perovskite solar cells still suffer from significant non-radiative recombination losses at the perovskite surface and across the perovskite/C₆₀ interface, limiting the future development of perovskite-based single- and multi-junction photovoltaics. Therefore, more effective inter- or transport layers are urgently required. To tackle these recombination losses, we introduce ortho-carborane as an interlayer material that has a spherical molecular structure and a three-dimensional aromaticity. Based on a variety of experimental techniques, we show that ortho-carborane decorated with phenylamino groups effectively passivates the perovskite surface and essentially eliminates the non-radiative recombination loss across the perovskite/C₆₀ interface with high thermal stability. We further demonstrate the potential of carborane as an electron transport material, facilitating electron extraction while blocking holes from the interface. The resulting inverted perovskite solar cells deliver a power conversion efficiency of over 23% with a low non-radiative voltage loss of 110 mV, and retain >97% of the initial efficiency after 400 h of maximum power point tracking. Overall, the designed carborane based interlayer simultaneously enables passivation, electron-transport and hole-blocking and paves the way toward more efficient and stable perovskite solar cells. Y1 - 2022 U6 - https://doi.org/10.1038/s41467-022-34203-x SN - 2041-1723 VL - 13 IS - 1 PB - Springer Nature CY - London ER - TY - JOUR A1 - Yazmaciyan, Aren A1 - Stolterfoht, Martin A1 - Burn, Paul L. A1 - Lin, Qianqian A1 - Meredith, Paul A1 - Armin, Ardalan T1 - Recombination losses above and below the transport percolation threshold in bulk heterojunction organic solar cells JF - Advanced energy materials N2 - Achieving the highest power conversion efficiencies in bulk heterojunction organic solar cells requires a morphology that delivers electron and hole percolation pathways for optimized transport, plus sufficient donor:acceptor contact area for near unity charge transfer state formation. This is a significant structural challenge, particularly in semiconducting polymer:fullerene systems. This balancing act in the model high efficiency PTB7:PC70BM blend is studied by tuning the donor:acceptor ratio, with a view to understanding the recombination loss mechanisms above and below the fullerene transport percolation threshold. The internal quantum efficiency is found to be strongly correlated to the slower carrier mobility in agreement with other recent studies. Furthermore, second-order recombination losses dominate the shape of the current density-voltage curve in efficient blend combinations, where the fullerene phase is percolated. However, below the charge transport percolation threshold, there is an electric-field dependence of first-order losses, which includes electric-field-dependent photogeneration. In the intermediate regime, the fill factor appears to be limited by both first- and second-order losses. These findings provide additional basic understanding of the interplay between the bulk heterojunction morphology and the order of recombination in organic solar cells. They also shed light on the limitations of widely used transport models below the percolation threshold. KW - bulk heterojunctions KW - charge transport KW - organic solar cells KW - percolation threshold KW - recombination losses Y1 - 2018 U6 - https://doi.org/10.1002/aenm.201703339 SN - 1614-6832 SN - 1614-6840 VL - 8 IS - 18 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Yang, Xiaohui A1 - Müller, David C. A1 - Neher, Dieter A1 - Meerholz, Klaus T1 - Highly efficient polymeric electrophosphorescent diodes N2 - Polymeric electrophosphorescent LEDs with internal quantum efficiencies approaching unity have been fabricated. Such performance levels are previously unknown for OLEDs. The key to this success is redox chemically doped oxetane- crosslinkable hole-transporting layers with multilayer capability (see figure). They improve hole injection and act as electron-blocking layers, without the need to include exciton-or hole-blocking layers Y1 - 2006 UR - 1960 = DOI: 10.1002/adma.200501867 ER - TY - JOUR A1 - Yang, Xiao Hui A1 - Jaiser, Frank A1 - Stiller, Burkhard A1 - Neher, Dieter A1 - Galbrecht, Frank A1 - Scherf, Ullrich T1 - Efficient polymer electrophosphoreseent devices with interfacial layers JF - Advanced functional materials N2 - It is shown that several polymers can form insoluble interfacial layers on a poly (ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) layer after annealing of the double-layer structure. The thickness of the interlayer is dependent on the characteristics of the underlying PEDOT.PSS and the molecular weight of the polymers. It is further shown that the electronic structures of the interlayer polymers have a significant effect on the properties of red-light-emitting polymer-based electrophosphorescent devices. Upon increasing the highest occupied molecular orbital and lowest unoccupied molecular orbital positions, a significant increase in current density and device efficiency is observed. This is attributed to efficient blocking of electrons in combination with direct injection of holes from the interlayer to the phosphorescent dye. Upon proper choice of the interlayer polymer, efficient red, polymer-based electrophosphorescent devices with a peak luminance efficiency of 5.5 cd A(-1) (external quantum efficiency = 6 %) and a maximum power-conversion efficiency of 5 Im W-1 can be realized. Y1 - 2006 U6 - https://doi.org/10.1002/adfm.200500834 SN - 1616-301X SN - 1616-3028 VL - 16 IS - 16 SP - 2156 EP - 2162 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Yang, Xiao Hui A1 - Jaiser, Frank A1 - Neher, Dieter A1 - Lawson, PaDreyia V. A1 - Brédas, Jean-Luc A1 - Zojer, Egbert A1 - Güntner, Roland A1 - Scanduicci de Freitas, Patricia A1 - Forster, Michael A1 - Scherf, Ullrich T1 - Suppression of the keto-emission in polyfluorene light-emitting diodes : Experiments and models N2 - The spectral characteristics of polyfluorene (PF)-based light-emitting diodes (LEDs) containing a defined low concentration of either keto-defects or of the polymer poly(9.9-octylfuorene-co-benzothiadiazole) (F8BT) are preseneted. Both types of blend layers were tested in different device configurations with respect to the relative and absolute intensities of green blue emission components. It is shown that blending hole-transporting molecules into the emission layer at low concentration or incorporation of a suitable hole-transport layer reduces the green emission contribution in the electroluminescence (EL) spectrum of the PF:F8BT blend, which is similar to what is observed for the keto- containing PF layer. We conclude that the keto-defects in PF homopolymer layers mainly constitute weakly emissive electron traps, in agreement with the results of quantum-mechanical calculations Y1 - 2004 SN - 1616-301X ER - TY - JOUR A1 - Yang, X. H. A1 - Neher, Dieter A1 - Hertel, D. A1 - Daubler, T. K. T1 - Highly efficient single-layer polymer electrophosphorescent devices N2 - A commercially available Ir complex has been employed for the preparation of highly efficient (see Figure) single-layer phosphorescent polymer light,emitting diodes by use of appropriate thermal treatment and proper adjustment of the layer composition. These devices exhibit essentially no dependence of the driving field on the concentration of the Ir complex, suggesting that the build-up of space-charge in the layer is insignificant Y1 - 2004 SN - 0935-9648 ER - TY - JOUR A1 - Yang, X. H. A1 - Neher, Dieter T1 - Polymer electrophosphorescence devices with high power conversion efficiencies N2 - We demonstrate efficient single-layer polymer phosphorescent light-emitting devices based on a green-emitting iridium complex and a polymer host co-doped with electron-transporting and hole-transporting molecules. These devices can be operated at relatively low voltages, resulting in a power conversion efficiency of up to 24 lm/W at luminous efficiencies exceeding 30 cd/A. The overall performances of these devices suggest that efficient electrophosphorescent devices with acceptable operating voltages can be achieved in very simple device structures fabricated by spin coating. (C) 2004 American Institute of Physics Y1 - 2004 SN - 0003-6951 ER - TY - JOUR A1 - Yang, X. H. A1 - Jaiser, Frank A1 - Klinger, S A1 - Neher, Dieter T1 - Blue polymer electrophosphorescent devices with different electron-transporting oxadiazoles N2 - We report that the performances of blue polymer electrophosphorescent devices are crucially depending on the choice of the electron transporting material incorporated into the emissive layer. Devices with 1,3-bis[(4-tert- butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7) doped at similar to 40 wt% into a poly(vinylcarbazole) matrix exhibited significantly higher efficiencies than those with 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), yielding maximum luminous and power efficiency values of 18.2 Cd/A and 8.8 lm/W, respectively. Time resolved photoluminescence measurements revealed a long lifetime phosphorescence component in layers with PBD, which we assign to significant triplet harvesting by this electron-transporting component. (c) 2006 American Institute of Physics Y1 - 2006 UR - http://scitation.aip.org/getpdf/servlet/ GetPDFServlet?filetype=pdf&id=APPLAB000088000002021107000001&idtype=cvips&doi=10.1063/1.2162693&prog=normal U6 - https://doi.org/10.1063/1.2162693 ER - TY - JOUR A1 - Yang, Jie A1 - Zhu, Xiaolei A1 - Wolf, Thomas J. A. A1 - Li, Zheng A1 - Nunes, João Pedro Figueira A1 - Coffee, Ryan A1 - Cryan, James P. A1 - Gühr, Markus A1 - Hegazy, Kareem A1 - Heinz, Tony F. A1 - Jobe, Keith A1 - Li, Renkai A1 - Shen, Xiaozhe A1 - Veccione, Theodore A1 - Weathersby, Stephen A1 - Wilkin, Kyle J. A1 - Yoneda, Charles A1 - Zheng, Qiang A1 - Martinez, Todd J. A1 - Centurion, Martin A1 - Wang, Xijie T1 - Imaging CF3I conical intersection and photodissociation dynamics with ultrafast electron diffraction JF - Science N2 - Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF3I molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF3 fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations. Y1 - 2018 U6 - https://doi.org/10.1126/science.aat0049 SN - 0036-8075 SN - 1095-9203 VL - 361 IS - 6397 SP - 64 EP - 67 PB - American Assoc. for the Advancement of Science CY - Washington ER - TY - JOUR A1 - Yang, Jie A1 - Gühr, Markus A1 - Vecchione, Theodore A1 - Robinson, Matthew Scott A1 - Li, Renkai A1 - Hartmann, Nick A1 - Shen, Xiaozhe A1 - Coffee, Ryan A1 - Corbett, Jeff A1 - Fry, Alan A1 - Gaffney, Kelly A1 - Gorkhover, Tais A1 - Hast, Carsten A1 - Jobe, Keith A1 - Makasyuk, Igor A1 - Reid, Alexander A1 - Robinson, Joseph A1 - Vetter, Sharon A1 - Wang, Fenglin A1 - Weathersby, Stephen A1 - Yoneda, Charles A1 - Wang, Xijie A1 - Centurion, Martin T1 - Femtosecond gas phase electron diffraction with MeV electrons JF - Faraday discussions N2 - We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution. Y1 - 2016 U6 - https://doi.org/10.1039/c6fd00071a SN - 1359-6640 SN - 1364-5498 VL - 194 SP - 563 EP - 581 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Yang, Jie A1 - Gühr, Markus A1 - Vecchione, Theodore A1 - Robinson, Matthew Scott A1 - Li, Renkai A1 - Hartmann, Nick A1 - Shen, Xiaozhe A1 - Coffee, Ryan A1 - Corbett, Jeff A1 - Fry, Alan A1 - Gaffney, Kelly A1 - Gorkhover, Tais A1 - Hast, Carsten A1 - Jobe, Keith A1 - Makasyuk, Igor A1 - Reid, Alexander A1 - Robinson, Joseph A1 - Vetter, Sharon A1 - Wang, Fenglin A1 - Weathersby, Stephen A1 - Yoneda, Charles A1 - Centurion, Martin A1 - Wang, Xijie T1 - Diffractive imaging of a rotational wavepacket in nitrogen molecules with femtosecond megaelectronvolt electron pulses JF - Nature Communications N2 - Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angstrom spatial precision is one of the critical challenges in the chemical sciences, as the nuclear geometry changes determine the molecular reactivity. For photoexcited molecules, the nuclear dynamics determine the photoenergy conversion path and efficiency. Here we report a gas-phase electron diffraction experiment using megaelectronvolt (MeV) electrons, where we captured the rotational wavepacket dynamics of nonadiabatically laser-aligned nitrogen molecules. We achieved a combination of 100 fs root-mean-squared temporal resolution and sub-Angstrom (0.76 angstrom) spatial resolution that makes it possible to resolve the position of the nuclei within the molecule. In addition, the diffraction patterns reveal the angular distribution of the molecules, which changes from prolate (aligned) to oblate (anti-aligned) in 300 fs. Our results demonstrate a significant and promising step towards making atomically resolved movies of molecular reactions. Y1 - 2016 U6 - https://doi.org/10.1038/ncomms11232 SN - 2041-1723 VL - 7 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Yang, Jie A1 - Guehr, Markus A1 - Shen, Xiaozhe A1 - Li, Renkai A1 - Vecchione, Theodore A1 - Coffee, Ryan A1 - Corbett, Jeff A1 - Fry, Alan A1 - Hartmann, Nick A1 - Hast, Carsten A1 - Hegazy, Kareem A1 - Jobe, Keith A1 - Makasyuk, Igor A1 - Robinson, Joseph A1 - Robinson, Matthew Scott A1 - Vetter, Sharon A1 - Weathersby, Stephen A1 - Yoneda, Charles A1 - Wang, Xijie A1 - Centurion, Martin T1 - Diffractive Imaging of Coherent Nuclear Motion in Isolated Molecules JF - Physical review letters N2 - Observing the motion of the nuclear wave packets during a molecular reaction, in both space and time, is crucial for understanding and controlling the outcome of photoinduced chemical reactions. We have imaged the motion of a vibrational wave packet in isolated iodine molecules using ultrafast electron diffraction with relativistic electrons. The time-varying interatomic distance was measured with a precision 0.07 angstrom and temporal resolution of 230 fs full width at half maximum. The method is not only sensitive to the position but also the shape of the nuclear wave packet. Y1 - 2016 U6 - https://doi.org/10.1103/PhysRevLett.117.153002 SN - 0031-9007 SN - 1079-7114 VL - 117 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Yang, Dong A1 - Eisert, Jens T1 - Entanglement combing N2 - We show that all multipartite pure states can, under local operations, be transformed into bipartite pairwise entangled states in a "lossless fashion": An arbitrary distinguished party will keep pairwise entanglement with all other parties after the asymptotic protocol-decorrelating all other parties from each other-in a way that the degree of entanglement of this party with respect to the rest will remain entirely unchanged. The set of possible entanglement distributions of bipartite pairs is also classified. Finally, we point out several applications of this protocol as a useful primitive in quantum information theory. Y1 - 2009 UR - http://prl.aps.org/ U6 - https://doi.org/10.1103/Physrevlett.103.220501 SN - 0031-9007 ER - TY - JOUR A1 - Yang, C. A1 - Vardeny, Z. V. A1 - Köhler, Anna A1 - Wohlgenannt, M. A1 - Al-Suti, Mohammed K. A1 - Khan, Muhammad S. T1 - Spectroscopic study of spin-dependent exciton formation rates in pi-conjugated semiconductors : Comparison with electroluminescence techniques N2 - It has been found in recent measurements that the singlet-to-triplet exciton ratio in organic light-emitting diodes (OLEDs) is larger than expected from spin degeneracy, and that singlet excitons form at a larger rate than triplets. We employed the technique of optically detected magnetic resonance to measure the spin-dependent exciton formation rates in films of a polymer and corresponding monomer, and explore the relation between the formation rates and the actual singlet-to-triplet ratio measured previously in OLEDs. We found that the spin-dependent exciton formation rates can indeed quantitatively explain the observed exciton yields, and that singlet formation rates and yields are significantly enhanced only in polymer OLEDs, but not in OLEDs made from the corresponding monomer Y1 - 2004 ER - TY - JOUR A1 - Yan, Xiaoli A1 - Xue, Zhike A1 - Jiang, Chaowei A1 - Priest, E. R. A1 - Kliem, Bernhard A1 - Yang, Liheng A1 - Wang, Jincheng A1 - Kong, Defang A1 - Song, Yongliang A1 - Feng, Xueshang A1 - Liu, Zhong T1 - Fast plasmoid-mediated reconnection in a solar flare JF - Nature Communications N2 - Magnetic reconnection is a multi-faceted process of energy conversion in astrophysical, space and laboratory plasmas that operates at microscopic scales but has macroscopic drivers and consequences. Solar flares present a key laboratory for its study, leaving imprints of the microscopic physics in radiation spectra and allowing the macroscopic evolution to be imaged, yet a full observational characterization remains elusive. Here we combine high resolution imaging and spectral observations of a confined solar flare at multiple wavelengths with data-constrained magnetohydrodynamic modeling to study the dynamics of the flare plasma from the current sheet to the plasmoid scale. The analysis suggests that the flare resulted from the interaction of a twisted magnetic flux rope surrounding a filament with nearby magnetic loops whose feet are anchored in chromospheric fibrils. Bright cusp-shaped structures represent the region around a reconnecting separator or quasi-separator (hyperbolic flux tube). The fast reconnection, which is relevant for other astrophysical environments, revealed plasmoids in the current sheet and separatrices and associated unresolved turbulent motions. Solar flares provide wide range of observational details about fundamental processes involved. Here, the authors show evidence for magnetic reconnection in a strong confined solar flare displaying all four reconnection flows with plasmoids in the current sheet and the separatrices. Y1 - 2022 U6 - https://doi.org/10.1038/s41467-022-28269-w SN - 2041-1723 VL - 13 IS - 1 PB - Nature Publishing Group UK CY - London ER - TY - JOUR A1 - Yan, Shengjie A1 - Liang, Yingjie A1 - Xu, Wei T1 - Characterization of chloride ions diffusion in concrete using fractional Brownian motion run with power law clock JF - Fractals : complex geometry, patterns, and scaling in nature and society N2 - In this paper, we propose a revised fractional Brownian motion run with a nonlinear clock (fBm-nlc) model and utilize it to illustrate the microscopic mechanism analysis of the fractal derivative diffusion model with variable coefficient (VC-FDM). The power-law mean squared displacement (MSD) links the fBm-nlc model and the VC-FDM via the two-parameter power law clock and the Hurst exponent is 0.5. The MSD is verified by using the experimental points of the chloride ions diffusion in concrete. When compared to the linear Brownian motion, the results show that the power law MSD of the fBm-nlc is much better in fitting the experimental points of chloride ions in concrete. The fBm-nlc clearly interprets the VC-FDM and provides a microscopic strategy in characterizing different types of non-Fickian diffusion processes with more different nonlinear functions. KW - mean squared displacement KW - anomalous diffusion KW - fractal derivative KW - fractional brownian motion KW - nonlinear clock Y1 - 2022 U6 - https://doi.org/10.1142/S0218348X22501778 SN - 0218-348X SN - 1793-6543 VL - 30 IS - 9 PB - World Scient. Publ. CY - Singapore [u.a.] ER - TY - JOUR A1 - Yamazaki, Yosuke A1 - Stolle, Claudia A1 - Matzka, Jürgen A1 - Siddiqui, Tarique Adnan A1 - Luehr, Hermann A1 - Alken, Patrick T1 - Longitudinal Variation of the Lunar Tide in the Equatorial Electrojet JF - Journal of geophysical research : Space physics N2 - The atmospheric lunar tide is one known source of ionospheric variability. The subject received renewed attention as recent studies found a link between stratospheric sudden warmings and amplified lunar tidal perturbations in the equatorial ionosphere. There is increasing evidence from ground observations that the lunar tidal influence on the ionosphere depends on longitude. We use magnetic field measurements from the CHAMP satellite during July 2000 to September 2010 and from the two Swarm satellites during November 2013 to February 2017 to determine, for the first time, the complete seasonal- longitudinal climatology of the semidiurnal lunar tidal variation in the equatorial electrojet intensity. Significant longitudinal variability is found in the amplitude of the lunar tidal variation, while the longitudinal variability in the phase is small. The amplitude peaks in the Peruvian sector (similar to 285 degrees E) during the Northern Hemisphere winter and equinoxes, and in the Brazilian sector (similar to 325 degrees E) during the Northern Hemisphere summer. There are also local amplitude maxima at similar to 55 degrees E and similar to 120 degrees E. The longitudinal variation is partly due to the modulation of ionospheric conductivities by the inhomogeneous geomagnetic field. Another possible cause of the longitudinal variability is neutral wind forcing by nonmigrating lunar tides. A tidal spectrum analysis of the semidiurnal lunar tidal variation in the equatorial electrojet reveals the dominance of the westward propagating mode with zonal wave number 2 (SW2), with secondary contributions by westward propagating modes with zonal wave numbers 3 (SW3) and 4 (SW4). Eastward propagating waves are largely absent from the tidal spectrum. Further study will be required for the relative importance of ionospheric conductivities and nonmigrating lunar tides. Y1 - 2017 U6 - https://doi.org/10.1002/2017JA024601 SN - 2169-9380 SN - 2169-9402 VL - 122 SP - 12445 EP - 12463 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Yamazaki, Yosuke A1 - Matzka, Jürgen A1 - Stolle, Claudia A1 - Kervalishvili, Guram N. A1 - Rauberg, Jan A1 - Bronkalla, Oliver A1 - Morschhauser, Achim A1 - Bruinsma, Sean L. A1 - Shprits, Yuri A1 - Jackson, David R. T1 - Geomagnetic activity index Hpo JF - Geophysical research letters N2 - The geomagnetic activity index Kp is widely used but is restricted by low time resolution (3-hourly) and an upper limit. To address this, new geomagnetic activity indices, Hpo, are introduced. Similar to Kp, Hpo expresses the level of planetary geomagnetic activity in units of thirds (0o, 0+, 1-, 1o, 1+, 2-, horizontal ellipsis ) based on the magnitude of geomagnetic disturbances observed at subauroral observatories. Hpo has a higher time resolution than Kp. 30-min (Hp30) and 60-min (Hp60) indices are produced. The frequency distribution of Hpo is designed to be similar to that of Kp so that Hpo may be used as a higher time-resolution alternative to Kp. Unlike Kp, which is capped at 9o, Hpo is an open-ended index and thus can characterize severe geomagnetic storms more accurately. Hp30, Hp60 and corresponding linearly scaled ap30 and ap60 are available, in near real time, at the GFZ website (https://www.gfz-potsdam.de/en/hpo-index). KW - Hpo KW - Hp30 KW - Hp60 KW - apo KW - ap30 KW - ap60 Y1 - 2022 U6 - https://doi.org/10.1029/2022GL098860 SN - 0094-8276 SN - 1944-8007 VL - 49 IS - 10 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Yadavalli, Nataraja Sekhar A1 - Saphiannikova, Marina A1 - Santer, Svetlana T1 - Photosensitive response of azobenzene containing films towards pure intensity or polarization interference patterns JF - Applied physics letters N2 - In this paper, we report on differences in the response of photosensitive azobenzene containing films upon irradiation with the intensity or polarization interference patterns. Two materials are studied differing in the molecular weight: an azobenzene-containing polymer and a molecular glass formed from a much smaller molecule consisting of three connected azobenzene units. Topography changes occurring along with the changes in irradiation conditions are recorded using a homemade set-up combining an optical part for generation and shaping of interference patterns and an atomic force microscope for acquiring the kinetics of film deformation. In this way, we could reveal the unique behavior of photosensitive materials during the first few minutes of irradiation: the change in topography is initially driven by an increase in the azobenzene free volume along with the transcis isomerization, followed by the mass transport finally resulting in the surface relief grating. This study demonstrates the great potential of our setup to experimentally highlight puzzling processes governing the formation of surface relief gratings. (C) 2014 AIP Publishing LLC. Y1 - 2014 U6 - https://doi.org/10.1063/1.4891615 SN - 0003-6951 SN - 1077-3118 VL - 105 IS - 5 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Yadavalli, Nataraja Sekhar A1 - Saphiannikova, Marina A1 - Lomadze, Nino A1 - Goldenberg, Leonid M. A1 - Santer, Svetlana T1 - Structuring of photosensitive material below diffraction limit using far field irradiation JF - Applied physics : A, Materials science & processing N2 - In this paper, we report on in-situ atomic force microscopy (AFM) studies of topographical changes in azobenzene-containing photosensitive polymer films that are irradiated with light interference patterns. We have developed an experimental setup consisting of an AFM combined with two-beam interferometry that permits us to switch between different polarization states of the two interfering beams while scanning the illuminated area of the polymer film, acquiring corresponding changes in topography in-situ. This way, we are able to analyze how the change in topography is related to the variation of the electrical field vector within the interference pattern. It is for the first time that with a rather simple experimental approach a rigorous assignment can be achieved. By performing in-situ measurements we found that for a certain polarization combination of two interfering beams [namely for the SP (a dagger center dot, a dagger") polarization pattern] the topography forms surface relief grating with only half the period of the interference patterns. Exploiting this phenomenon we are able to fabricate surface relief structures with characteristic features measuring only 140 nm, by using far field optics with a wavelength of 491 nm. We believe that this relatively simple method could be extremely valuable to, for instance, produce structural features below the diffraction limit at high-throughput, and this could significantly contribute to the search of new fabrication strategies in electronics and photonics industry. Y1 - 2013 U6 - https://doi.org/10.1007/s00339-013-7945-3 SN - 0947-8396 SN - 1432-0630 VL - 113 IS - 2 SP - 263 EP - 272 PB - Springer CY - New York ER - TY - JOUR A1 - Yadavalli, Nataraja Sekhar A1 - Santer, Svetlana T1 - In-situ atomic force microscopy study of the mechanism of surface relief grating formation in photosensitive polymer films JF - Journal of applied physics N2 - When photosensitive azobenzene-containing polymer films are irradiated with light interference patterns, topographic variations in the film develop that follow the local distribution of the electric field vector. The exact correspondence of e.g., the vector orientation in relation to the presence of local topographic minima or maxima is in general difficult to determine. Here, we report on a systematic procedure how this can be accomplished. For this, we devise a new set-up combining an atomic force microscope and two-beam interferometry. With this set-up, it is possible to track the topography change in-situ, while at the same time changing polarization and phase of the impinging interference pattern. This is the first time that an absolute correspondence between the local distribution of electric field vectors and the local topography of the relief grating could be established exhaustively. Our setup does not require a complex mathematical post-processing and its simplicity renders it interesting for characterizing photosensitive polymer films in general. Y1 - 2013 U6 - https://doi.org/10.1063/1.4809640 SN - 0021-8979 SN - 1089-7550 VL - 113 IS - 22 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Yadavalli, Nataraja Sekhar A1 - Loebner, Sarah A1 - Papke, Thomas A1 - Sava, Elena A1 - Hurduc, Nicolae A1 - Santer, Svetlana T1 - A comparative study of photoinduced deformation in azobenzene containing polymer films JF - Soft matter N2 - In this paper two groups supporting different views on the mechanism of light induced polymer deformation argue about the respective underlying theoretical conceptions, in order to bring this interesting debate to the attention of the scientific community. The group of Prof. Nicolae Hurduc supports the model claiming that the cyclic isomerization of azobenzenes may cause an athermal transition of the glassy azobenzene containing polymer into a fluid state, the so-called photo-fluidization concept. This concept is quite convenient for an intuitive understanding of the deformation process as an anisotropic flow of the polymer material. The group of Prof. Svetlana Santer supports the re-orientational model where the mass-transport of the polymer material accomplished during polymer deformation is stated to be generated by the light-induced re-orientation of the azobenzene side chains and as a consequence of the polymer backbone that in turn results in local mechanical stress, which is enough to irreversibly deform an azobenzene containing material even in the glassy state. For the debate we chose three polymers differing in the glass transition temperature, 32 degrees C, 87 degrees C and 95 degrees C, representing extreme cases of flexible and rigid materials. Polymer film deformation occurring during irradiation with different interference patterns is recorded using a homemade set-up combining an optical part for the generation of interference patterns and an atomic force microscope for acquiring the kinetics of film deformation. We also demonstrated the unique behaviour of azobenzene containing polymeric films to switch the topography in situ and reversibly by changing the irradiation conditions. We discuss the results of reversible deformation of three polymers induced by irradiation with intensity (IIP) and polarization (PIP) interference patterns, and the light of homogeneous intensity in terms of two approaches: the re-orientational and the photo-fluidization concepts. Both agree in that the formation of opto-mechanically induced stresses is a necessary prerequisite for the process of deformation. Using this argument, the deformation process can be characterized either as a flow or mass transport. Y1 - 2016 U6 - https://doi.org/10.1039/c6sm00029k SN - 1744-683X SN - 1744-6848 VL - 12 SP - 2593 EP - 2603 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Yadavalli, Nataraja Sekhar A1 - Linde, Felix A1 - Kopyshev, Alexey A1 - Santer, Svetlana T1 - Soft matter beats hard matter - rupturing of thin metallic films induced by mass transport in photosensitive polymer films JF - ACS applied materials & interfaces N2 - The interface between thin films of metal and polymer materials play a significant role in modern flexible microelectronics viz., metal contacts on polymer substrates, printed electronics and prosthetic devices. The major emphasis in metal polymer interface is on studying how the externally applied stress in the polymer substrate leads to the deformation and cracks in metal film and vice versa. Usually, the deformation process involves strains varying over large lateral dimensions because of excessive stress at local imperfections. Here we show that the seemingly random phenomena at macroscopic scales can be rendered rather controllable at submicrometer length scales. Recently, we have created a metal polymer interface system with strains varying over periods of several hundred nanometers. This was achieved by exploiting the formation of surface relief grating (SRG) within the azobenzene containing photosensitive polymer film upon irradiation with light interference pattern. Up to a thickness of 60 nm, the adsorbed metal film adapts neatly to the forming relief, until it ultimately ruptures into an array of stripes by formation of highly regular and uniform cracks along the maxima and minima of the polymer topography. This surprising phenomenon has far-reaching implications. This is the first time a direct probe is available to estimate the forces emerging in SRG formation in glassy polymers. Furthermore, crack formation in thin metal films can be studied literally in slow motion, which could lead to substantial improvements in the design process of flexible electronics. Finally, cracks are produced uniformly and at high density, contrary to common sense. This could offer new strategies for precise nanofabrication procedures mechanical in character. KW - metal/polymer interface KW - rupturing of metal film KW - forces generated during surface relief grating formation KW - in situ atomic force microscopy KW - azobenzene KW - two beam interferometry Y1 - 2013 U6 - https://doi.org/10.1021/am4006132w SN - 1944-8244 VL - 5 IS - 16 SP - 7743 EP - 7747 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Yadavalli, Nataraja Sekhar A1 - König, Tobias A1 - Santer, Svetlana T1 - Selective mass transport of azobenzene-containing photosensitive films towards or away from the light intensity JF - Journal of the Society for Information Display N2 - Here, we report on two photosensitive amorphous polymers showing opposite behavior upon exposure to illumination. The first polymer (PAZO) consists of linear backbone to which azobenzene-containing side chains are covalently attached, while in the second polymer (azo-PEI), the azobenzene side chains are attached ionically to a polyelectrolyte backbone. When irradiated through a mask, the PAZO goes away from the intensity maxima, leaving behind topography trenches, while the direction of the mass transport of the azo-PEI polymer points towards the intensity maxima. This kind of behavior has been reported only for certain liquid crystalline polymers that exhibit in-phase reaction on illumination, that is, topography maxima coincides with the intensity maxima. Furthermore, flat nanocrystals placed on top of azo-PEI film was found to be moved together with the mass transport of the underlying polymer film as visualized using in situ atomic force microscopy (AFM) measurements. It was also demonstrated that the two polymer films respond differently on irradiation with the polarization and intensity interference patterns (IPs). To record the kinetic of the surface relief grating formation within two polymers during irradiation with different IPs, we utilized a homemade setup combining the optical part for the generation of IP and AFM. A possible mechanism explaining different responses on the irradiation of amorphous polymers is discussed in the frame of a theoretical model proposed by Saphiannikova et al. (J. Phys. Chem. B 113, 5032-5045 (2009)). KW - azobenzene KW - surface relief grating KW - light-induced mass transport KW - interference pattern KW - nano-object motion Y1 - 2015 U6 - https://doi.org/10.1002/jsid.306 SN - 1071-0922 SN - 1938-3657 VL - 23 IS - 4 SP - 154 EP - 162 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Yadavalli, Nataraja Sekhar A1 - Korolkov, Denis A1 - Moulin, Jean-Francois A1 - Krutyeva, Margarita A1 - Santer, Svetlana T1 - Probing opto-mechanical stresses within azobenzene-containing photosensitive polymer films by a thin metal film placed above JF - ACS applied materials & interfaces N2 - Azo-modified photosensitive polymers offer the interesting possibility to reshape bulk polymers and thin films by UV-irradiation while being in the solid glassy state. The polymer undergoes considerable mass transport under irradiation with a light interference pattern resulting in the formation of surface relief grating (SRG). The forces inscribing this SRG pattern into a thin film are hard to assess experimentally directly. In the current study, we are proposing a method to probe opto-mechanical stresses within polymer films by characterizing the mechanical response of thin metal films (10 nm) deposited on the photosensitive polymer. During irradiation, the metal film not only deforms along with the SRG formation but ruptures in a regular and complex manner. The morphology of the cracks differs strongly depending on the electrical field distribution in the interference pattern, even when the magnitude and the kinetics of the strain are kept constant. This implies a complex local distribution of the opto-mechanical stress along the topography grating. In addition, the neutron reflectivity measurements of the metal/polymer interface indicate the penetration of a metal layer within the polymer, resulting in a formation of a bonding layer that confirms the transduction of light-induced stresses in the polymer layer to a metal film. KW - surface relief grating KW - opto-mechanical stresses KW - bonding layer at the metal/polymer interface KW - rupturing of metal film KW - metal/multilayered graphene/polymer interfaces KW - azobenzene Y1 - 2014 U6 - https://doi.org/10.1021/am501870t SN - 1944-8244 VL - 6 IS - 14 SP - 11333 EP - 11340 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Xue, Zhike A1 - Yan, Xiaoli A1 - Cheng, Xin A1 - Yang, Liheng A1 - Su, Yingna A1 - Kliem, Bernhard A1 - Zhang, Jun A1 - Liu, Zhong A1 - Bi, Yi A1 - Xiang, Yongyuan A1 - Yang, Kai A1 - Zhao, Li T1 - Observing the release of twist by magnetic reconnection in a solar filament eruption JF - Nature Communications N2 - Magnetic reconnection is a fundamental process of topology change and energy release, taking place in plasmas on the Sun, in space, in astrophysical objects and in the laboratory. However, observational evidence has been relatively rare and typically only partial. Here we present evidence of fast reconnection in a solar filament eruption using high-resolution H-alpha images from the New Vacuum Solar Telescope, supplemented by extreme ultraviolet observations. The reconnection is seen to occur between a set of ambient chromospheric fibrils and the filament itself. This allows for the relaxation of magnetic tension in the filament by an untwisting motion, demonstrating a flux rope structure. The topology change and untwisting are also found through nonlinear force-free field modelling of the active region in combination with magnetohydrodynamic simulation. These results demonstrate a new role for reconnection in solar eruptions: the release of magnetic twist. Y1 - 2016 U6 - https://doi.org/10.1038/ncomms11837 SN - 2041-1723 VL - 7 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Xue, Rui A1 - Liu, Ruo-Yu A1 - Wang, Xiang-Yu A1 - Yan, Huirong A1 - Böttcher, Markus T1 - On the minimum jet power of TeV BL Lac objects in the p-gamma model JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We study the requirement of the jet power in the conventional p-gamma models (photopion production and Bethe-Heitler pair production) for TeV BL Lac objects. We select a sample of TeV BL Lac objects whose spectral energy distributions are difficult to explain by the one-zone leptonic model. Based on the relation between the p-gamma interaction efficiency and the opacity of gamma gamma absorption, we find that the detection of TeV emission poses upper limits on the p-gamma interaction efficiencies in these sources and hence minimum jet powers can be derived accordingly. We find that the obtained minimum jet powers exceed the Eddington luminosity of the supermassive black holes (SMBHs). Implications for the accretion mode of the SMBHs in these BL Lac objects and the origin of their TeV emissions are discussed. KW - galaxies: active KW - galaxies: jets KW - radiation mechanisms: non-thermal Y1 - 2019 U6 - https://doi.org/10.3847/1538-4357/aaf720 SN - 0004-637X SN - 1538-4357 VL - 871 IS - 1 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Xu, Yong A1 - Liu, Xuemei A1 - Li, Yongge A1 - Metzler, Ralf T1 - Heterogeneous diffusion processes and nonergodicity with Gaussian colored noise in layered diffusivity landscapes JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - Heterogeneous diffusion processes (HDPs) with space-dependent diffusion coefficients D(x) are found in a number of real-world systems, such as for diffusion of macromolecules or submicron tracers in biological cells. Here, we examine HDPs in quenched-disorder systems with Gaussian colored noise (GCN) characterized by a diffusion coefficient with a power-law dependence on the particle position and with a spatially random scaling exponent. Typically, D(x) is considered to be centerd at the origin and the entire x axis is characterized by a single scaling exponent a. In this work we consider a spatially random scenario: in periodic intervals ("layers") in space D(x) is centerd to the midpoint of each interval. In each interval the scaling exponent alpha is randomly chosen from a Gaussian distribution. The effects of the variation of the scaling exponents, the periodicity of the domains ("layer thickness") of the diffusion coefficient in this stratified system, and the correlation time of the GCN are analyzed numerically in detail. We discuss the regimes of superdiffusion, subdiffusion, and normal diffusion realisable in this system. We observe and quantify the domains where nonergodic and non-Gaussian behaviors emerge in this system. Our results provide new insights into the understanding of weak ergodicity breaking for HDPs driven by colored noise, with potential applications in quenched layered systems, typical model systems for diffusion in biological cells and tissues, as well as for diffusion in geophysical systems. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevE.102.062106 SN - 2470-0045 SN - 2470-0053 VL - 102 IS - 6 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Xu, Siyao A1 - Yan, Huirong A1 - Lazarian, A. T1 - DAMPING OF MAGNETOHYDRODYNAMIC TURBULENCE IN PARTIALLY IONIZED PLASMA: IMPLICATIONS FOR COSMIC RAY PROPAGATION JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - We study the damping processes of both incompressible and compressible magnetohydrodynamic (MHD) turbulence in a partially ionized medium. We start from the linear analysis of MHD waves, applying both single-fluid and two-fluid treatments. The damping rates derived from the linear analysis are then used in determining the damping scales of MHD turbulence. The physical connection between the damping scale of MHD turbulence and the cutoff boundary of linear MHD waves is investigated. We find two branches of slow modes propagating in ions and neutrals, respectively, below the damping scale of slow MHD turbulence, and offer a thorough discussion of their propagation and dissipation behavior. Our analytical results are shown to be applicable in a variety of partially ionized interstellar medium (ISM) phases and the solar chromosphere. The importance of neutral viscosity in damping the Alfvenic turbulence in the interstellar warm neutral medium and the solar chromosphere is demonstrated. As a significant astrophysical utility, we introduce damping effects to the propagation of cosmic rays in partially ionized ISM. The important role of turbulence damping in both transit-time damping and gyroresonance is identified. KW - cosmic rays KW - magnetohydrodynamics (MHD) KW - turbulence Y1 - 2016 U6 - https://doi.org/10.3847/0004-637X/826/2/166 SN - 0004-637X SN - 1538-4357 VL - 826 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Xu, Pengbo A1 - Zhou, Tian A1 - Metzler, Ralf A1 - Deng, Weihua T1 - Lévy walk dynamics in an external harmonic potential JF - Physical review : E, Statistical, nonlinear, and soft matter physics N2 - Levy walks (LWs) are spatiotemporally coupled random-walk processes describing superdiffusive heat conduction in solids, propagation of light in disordered optical materials, motion of molecular motors in living cells, or motion of animals, humans, robots, and viruses. We here investigate a key feature of LWs-their response to an external harmonic potential. In this generic setting for confined motion we demonstrate that LWs equilibrate exponentially and may assume a bimodal stationary distribution. We also show that the stationary distribution has a horizontal slope next to a reflecting boundary placed at the origin, in contrast to correlated superdiffusive processes. Our results generalize LWs to confining forces and settle some longstanding puzzles around LWs. Y1 - 2020 U6 - https://doi.org/10.1103/PhysRevE.101.062127 SN - 2470-0045 SN - 2470-0053 SN - 1550-2376 SN - 1063-651X SN - 1539-3755 VL - 101 IS - 6 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Xu, Pengbo A1 - Zhou, Tian A1 - Metzler, Ralf A1 - Deng, Weihua T1 - Stochastic harmonic trapping of a Lévy walk BT - transport and first-passage dynamics under soft resetting strategies JF - New journal of physics : the open-access journal for physics / Deutsche Physikalische Gesellschaft ; IOP, Institute of Physics N2 - We introduce and study a Lévy walk (LW) model of particle spreading with a finite propagation speed combined with soft resets, stochastically occurring periods in which an harmonic external potential is switched on and forces the particle towards a specific position. Soft resets avoid instantaneous relocation of particles that in certain physical settings may be considered unphysical. Moreover, soft resets do not have a specific resetting point but lead the particle towards a resetting point by a restoring Hookean force. Depending on the exact choice for the LW waiting time density and the probability density of the periods when the harmonic potential is switched on, we demonstrate a rich emerging response behaviour including ballistic motion and superdiffusion. When the confinement periods of the soft-reset events are dominant, we observe a particle localisation with an associated non-equilibrium steady state. In this case the stationary particle probability density function turns out to acquire multimodal states. Our derivations are based on Markov chain ideas and LWs with multiple internal states, an approach that may be useful and flexible for the investigation of other generalised random walks with soft and hard resets. The spreading efficiency of soft-rest LWs is characterised by the first-passage time statistic. KW - diffusion KW - anomalous diffusion KW - stochastic resetting KW - Levy walks Y1 - 2022 U6 - https://doi.org/10.1088/1367-2630/ac5282 SN - 1367-2630 VL - 24 IS - 3 SP - 1 EP - 28 PB - Deutsche Physikalische Gesellschaft CY - Bad Honnef ER - TY - JOUR A1 - Xu, Pengbo A1 - Metzler, Ralf A1 - Wang, Wanli T1 - Infinite density and relaxation for Levy walks in an external potential BT - Hermite polynomial approach JF - Physical review N2 - Levy walks are continuous-time random-walk processes with a spatiotemporal coupling of jump lengths and waiting times. We here apply the Hermite polynomial method to study the behavior of LWs with power-law walking time density for four different cases. First we show that the known result for the infinite density of an unconfined, unbiased LW is consistently recovered. We then derive the asymptotic behavior of the probability density function (PDF) for LWs in a constant force field, and we obtain the corresponding qth-order moments. In a harmonic external potential we derive the relaxation dynamic of the LW. For the case of a Poissonian walking time an exponential relaxation behavior is shown to emerge. Conversely, a power-law decay is obtained when the mean walking time diverges. Finally, we consider the case of an unconfined, unbiased LW with decaying speed v(r ) = v0/./r. When the mean walking time is finite, a universal Gaussian law for the position-PDF of the walker is obtained explicitly. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevE.105.044118 SN - 2470-0045 SN - 2470-0053 VL - 105 IS - 4 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Xu, Pengbo A1 - Deng, Weihua A1 - Sandev, Trifce T1 - Levy walk with parameter dependent velocity BT - hermite polynomial approach and numerical simulation JF - Journal of physics : A, Mathematical and theoretical N2 - To analyze stochastic processes, one often uses integral transform (Fourier and Laplace) methods. However, for the time-space coupled cases, e.g. the Levy walk, sometimes the integral transform method may fail. Here we provide a Hermite polynomial expansion approach, being complementary to the integral transform method, to the Levy walk. Two approaches are compared for some already known results. We also consider the generalized Levy walk with parameter dependent velocity. Namely, we consider the Levy walk with velocity which depends on the walking length or on the duration of each step. Some interesting features of the generalized Levy walk are observed, including the special shapes of the probability density function, the first passage time distributions, and various diffusive behaviors of the mean squared displacement. KW - Hermite polynomial expansion KW - Levy walk KW - anomalous diffusion KW - parameter KW - dependent velocity Y1 - 2020 U6 - https://doi.org/10.1088/1751-8121/ab7420 SN - 1751-8113 SN - 1751-8121 VL - 53 IS - 11 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Xu, Jingsan A1 - Shalom, Menny A1 - Piersimoni, Fortunato A1 - Antonietti, Markus A1 - Neher, Dieter A1 - Brenner, Thomas J. K. T1 - Color-Tunable Photoluminescence and NIR Electroluminescence in Carbon Nitride Thin Films and Light-Emitting Diodes JF - Advanced optical materials Y1 - 2015 U6 - https://doi.org/10.1002/adom.201500019 SN - 2195-1071 VL - 3 IS - 7 SP - 913 EP - 917 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Xu, Jingsan A1 - Cao, Shaowen A1 - Brenner, Thomas J. K. A1 - Yang, Xiaofei A1 - Yu, Jiaguo A1 - Antonietti, Markus A1 - Shalom, Menny T1 - Supramolecular Chemistry in Molten Sulfur: Preorganization Effects Leading to Marked Enhancement of Carbon Nitride Photoelectrochemistry JF - Advanced functional materials N2 - Here, a new method for enhancing the photoelectrochemical properties of carbon nitride thin films by in situ supramolecular-driven preorganization of phenyl-contained monomers in molten sulfur is reported. A detailed analysis of the chemical and photophysical properties suggests that the molten sulfur can texture the growth and induce more effective integration of phenyl groups into the carbon nitride electrodes, resulting in extended light absorption alongside with improved conductivity and better charge transfer. Furthermore, photophysical measurements indicate the formation of sub-bands in the optical bandgap which is beneficial for exciton splitting. Moreover, the new bands can mediate hole transfer to the electrolyte, thus improving the photooxidation activity. The utilization of high temperature solvent as the polymerization medium opens new opportunities for the significant improvement of carbon nitride films toward an efficient photoactive material for various applications. KW - carbon nitride thin film KW - charge transfer KW - molten sulfur KW - photoelectrochemistry Y1 - 2015 U6 - https://doi.org/10.1002/adfm.201502843 SN - 1616-301X SN - 1616-3028 VL - 25 IS - 39 SP - 6265 EP - 6271 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Xu, Jingsan A1 - Brenner, Thomas J. K. A1 - Chen, Zupeng A1 - Neher, Dieter A1 - Antonietti, Markus A1 - Shalom, Menny T1 - Upconversion-agent induced improvement of g-C3N4 photocatalyst under visible light JF - ACS applied materials & interfaces N2 - Herein, we report the use of upconversion agents to modify graphite carbon nitride (g-C3N4) by direct thermal condensation of a mixture of ErCl3 center dot 6H(2)O and the supramolecular precursor cyanuric acid-melamine. We show the enhancement of g-C3N4 photoactivity after Er3+ doping by monitoring the photodegradation of Rhodamine B dye under visible light. The contribution of the upconversion agent is demonstrated by measurements using only a red laser. The Er3+ doping alters both the electronic and the chemical properties of g-C3N4. The Er3+ doping reduces emission intensity and lifetime, indicating the formation of new, nonradiative deactivation pathways, probably involving charge-transfer processes. KW - metal-free photocatalysis KW - upconversion KW - carbon nitride KW - RhB photodegradation Y1 - 2014 U6 - https://doi.org/10.1021/am5051263 SN - 1944-8244 VL - 6 IS - 19 SP - 16481 EP - 16486 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Xu, Jingsan A1 - Brenner, Thomas J. K. A1 - Chabanne, Laurent A1 - Neher, Dieter A1 - Antonietti, Markus A1 - Shalom, Menny T1 - Liquid-Based growth of polymeric carbon nitride layers and their use in a mesostructured polymer solar cell with V-oc exceeding 1 V JF - Journal of the American Chemical Society N2 - Herein we report a general liquid-mediated pathway for the growth of continuous polymeric carbon nitride (C3N4) thin films. The deposition method consists of the use of supramolecular complexes that transform to the liquid state before direct thermal condensation into C3N4 solid films. The resulting films exhibit continuous porous C3N4 networks on various substrates. Moreover, the optical absorption can be easily tuned to cover the solar spectrum by the insertion of an additional molecule into the starting complex. The strength of the deposition method is demonstrated by the use of the C3N4 layer as the electron acceptor in a polymer solar cell that exhibits a remarkable open-circuit voltage exceeding 1 V. The easy, safe, and direct synthesis of carbon nitride in a continuous layered architecture on different functional substrates opens new possibilities for the fabrication of many energy-related devices. Y1 - 2014 U6 - https://doi.org/10.1021/ja508329c SN - 0002-7863 VL - 136 IS - 39 SP - 13486 EP - 13489 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Xiong, Hui A1 - Mignolet, Benoit A1 - Fang, Li A1 - Osipov, Timur A1 - Wolf, Thomas J. A. A1 - Sistrunk, Emily A1 - Gühr, Markus A1 - Remacle, Francoise A1 - Berrah, Nora T1 - The Role of Super-Atom Molecular Orbitals in Doped Fullerenes in a Femtosecond Intense Laser Field JF - Scientific reports N2 - The interaction of gas phase endohedral fullerene Ho3N@C-80 with intense (0.1-5 x 10(14) W/cm(2)), short (30 fs), 800 nm laser pulses was investigated. The power law dependence of Ho3N@C-80(q+), q = 1-2, was found to be different from that of C-60. Time-dependent density functional theory computations revealed different light-induced ionization mechanisms. Unlike in C-60, in doped fullerenes, the breaking of the cage spherical symmetry makes super atomic molecular orbital (SAMO) states optically active. Theoretical calculations suggest that the fast ionization of the SAMO states in Ho3N@C-80 is responsible for the n = 3 power law for singly charged parent molecules at intensities lower than 1.2 x 10(14) W/cm(2). Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-00124-9 SN - 2045-2322 VL - 7 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Xiong, Hui A1 - Fang, Li A1 - Osipov, Timur A1 - Kling, Nora G. A1 - Wolf, Thomas J. A. A1 - Sistrunk, Emily A1 - Obaid, Razib A1 - Gühr, Markus A1 - Berrah, Nora T1 - Fragmentation of endohedral fullerene Ho3N@C-80 in an intense femtosecond near-infrared laser field JF - Physical review : A, Atomic, molecular, and optical physics N2 - The fragmentation of gas phase endohedral fullerene, Ho3N@C-80, was investigated using femtosecond near-infrared laser pulses with an ion velocity map imaging spectrometer. We observed that Ho+ abundance associated with carbon cage opening dominates at an intensity of 1.1 x 10(14) W/cm(2). As the intensity increases, the Ho+ yield associated with multifragmentation of the carbon cage exceeds the prominence of Ho+ associated with the gentler carbon cage opening. Moreover, the power law dependence of Ho+ on laser intensity indicates that the transition of the most likely fragmentation mechanisms occurs around 2.0 x 10(14) W/cm(2). Y1 - 2018 U6 - https://doi.org/10.1103/PhysRevA.97.023419 SN - 2469-9926 SN - 2469-9934 VL - 97 IS - 2 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Xiong, Chao A1 - Stolle, Claudia A1 - Lühr, Hermann T1 - The Swarm satellite loss of GPS signal and its relation to ionospheric plasma irregularities JF - Space Weather: The International Journal of Research and Applications N2 - In this study we investigated conditions for loss of GPS signals observed by the Swarm satellites during a 2 year period, from December 2013 to November 2015. Our result shows that the Swarm satellites encountered most of the total loss of GPS signal at the ionization anomaly crests, between +/- 5 degrees and +/- 20 degrees magnetic latitude, forming two bands along the magnetic equator, and these low-latitude events mainly appear around postsunset hours from 19: 00 to 22: 00 local time. By further checking the in situ electron density measurements of Swarm, we found that practically, all the total loss of GPS signal events at low latitudes are related to equatorial plasma irregularities (EPIs) that show absolute density depletions larger than 10 x 10(11) m(-3); then, the Swarm satellites encountered for up to 95% loss of GPS signal for at least one channel and up to 45% tracked less than four GPS satellites (making precise orbit determination impossible). For those EPIs with density depletions less than 10 x 10(11) m(-3), the chance of tracked GPS signals less than four reduces to only 1.0%. Swarm also observed total loss of all GPS signal at high latitudes, mainly around local noon, and these events are related to large spatial density gradients due to polar patches or increased geomagnetic/auroral activities. We further found that the loss of GPS signals were less frequent after appropriate settings of the Swarm GPS receivers had been updated. However, the more recent period of the mission, e.g., after the GPS receiver settings have been updated, also coincides with less severe electron density depletions due to the declining solar cycle, making GPS loss events less likely. We conclude that both lower electron density gradients and appropriate GPS receiver settings reduce the probability for Swarm satellites loss of GPS signals. Y1 - 2016 U6 - https://doi.org/10.1002/2016SW001439 SN - 1542-7390 VL - 14 SP - 563 EP - 577 PB - American Geophysical Union CY - Washington ER -