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    Single Molecule Magnetism with Strong Magnetic Anisotropy and Enhanced Dy∙∙∙Dy Coupling in Three Isomers of Dy-Oxide Clusterfullerene Dy2O@C82
    (Chichester : John Wiley and Sons Ltd, 2019) Yang, W.; Velkos, G.; Liu, F.; Sudarkova, S.M.; Wang, Y.; Zhuang, J.; Zhang, H.; Li, X.; Zhang, X.; Büchner, B.; Avdoshenko, S.M.; Popov, A.A.; Chen, N.
    A new class of single-molecule magnets (SMMs) based on Dy-oxide clusterfullerenes is synthesized. Three isomers of Dy2O@C82 with Cs(6), C3v(8), and C2v(9) cage symmetries are characterized by single-crystal X-ray diffraction, which shows that the endohedral Dy−(µ2-O)−Dy cluster has bent shape with very short Dy−O bonds. Dy2O@C82 isomers show SMM behavior with broad magnetic hysteresis, but the temperature and magnetization relaxation depend strongly on the fullerene cage. The short Dy−O distances and the large negative charge of the oxide ion in Dy2O@C82 result in the very strong magnetic anisotropy of Dy ions. Their magnetic moments are aligned along the Dy−O bonds and are antiferromagnetically (AFM) coupled. At low temperatures, relaxation of magnetization in Dy2O@C82 proceeds via the ferromagnetically (FM)-coupled excited state, giving Arrhenius behavior with the effective barriers equal to the AFM-FM energy difference. The AFM-FM energy differences of 5.4–12.9 cm−1 in Dy2O@C82 are considerably larger than in SMMs with {Dy2O2} bridges, and the Dy∙∙∙Dy exchange coupling in Dy2O@C82 is the strongest among all dinuclear Dy SMMs with diamagnetic bridges. Dy-oxide clusterfullerenes provide a playground for the further tuning of molecular magnetism via variation of the size and shape of the fullerene cage.
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    Measurements of gaseous H2SO4 by AP-ID-CIMS during CAREBeijing 2008 Campaign
    (München : European Geopyhsical Union, 2011) Zheng, J.; Hu, M.; Zhang, R.; Yue, D.; Wang, Z.; Guo, S.; Li, X.; Bohn, B.; Shao, M.; He, L.; Huang, X.; Wiedensohler, A.; Zhu, T.
    As part of the 2008 Campaign of Air Quality Research in Beijing and Surrounding Regions (CAREBeijing 2008), measurements of gaseous sulfuric acid (H2SO4) have been conducted at an urban site in Beijing, China from 7 July to 25 September 2008 using atmospheric pressure ion drift – chemical ionization mass spectrometry (AP-ID-CIMS). This represents the first gaseous H2SO4 measurements in China. Diurnal profile of sulfuric acid is strongly dependent on the actinic flux, reaching a daily maximum around noontime and with an hourly average concentration of 5 × 106 molecules cm−3. Simulation of sulfuric acid on the basis of the measured sulfur dioxide concentration, photolysis rates of ozone and nitrogen dioxide, and aerosol surface areas captures the trend of the measured H2SO4 diurnal variation within the uncertainties, indicating that photochemical production and condensation onto preexisting particle surface dominate the observed diurnal H2SO4 profile. The frequency of the peak H2SO4 concentration exceeding 5 × 106 molecules cm−3 increases by 16 % during the period of the summer Olympic Games (8–24 August 2008), because of the implementation of air quality control regulations. Using a multivariate statistical method, the critical nucleus during nucleation events is inferred, containing two H2SO4 molecules (R2 = 0.85). The calculated condensation rate of H2SO4 can only account for 10–25 % of PM1 sulfate formation, indicating that either much stronger sulfate production exists at the SO2 source region or other sulfate production mechanisms are responsible for the sulfate production.
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    Exploring the atmospheric chemistry of nitrous acid (HONO) at a rural site in Southern China
    (München : European Geopyhsical Union, 2012) Li, X.; Brauers, T.; Häseler, R.; Bohn, B.; Fuchs, H.; Hofzumahaus, A.; Holland, F.; Lou, S.; Lu, K.D.; Rohrer, F.; Hu, M.; Zeng, L.M.; Zhang, Y.H.; Garland, R.M.; Su, H.; Nowak, A.; Wiedensohler, A.; Takegawa, N.; Shao, M.; Wahner, A.
    We performed measurements of nitrous acid (HONO) during the PRIDE-PRD2006 campaign in the Pearl River Delta region 60 km north of Guangzhou, China, for 4 weeks in June 2006. HONO was measured by a LOPAP in-situ instrument which was setup in one of the campaign supersites along with a variety of instruments measuring hydroxyl radicals, trace gases, aerosols, and meteorological parameters. Maximum diurnal HONO mixing ratios of 1–5 ppb were observed during the nights. We found that the nighttime build-up of HONO can be attributed to the heterogeneous NO2 to HONO conversion on ground surfaces and the OH + NO reaction. In addition to elevated nighttime mixing ratios, measured noontime values of ≈200 ppt indicate the existence of a daytime source higher than the OH + NO→HONO reaction. Using the simultaneously recorded OH, NO, and HONO photolysis frequency, a daytime additional source strength of HONO (PM) was calculated to be 0.77 ppb h−1 on average. This value compares well to previous measurements in other environments. Our analysis of PM provides evidence that the photolysis of HNO3 adsorbed on ground surfaces contributes to the HONO formation.
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    The simulations of sulfuric acid concentration and new particle formation in an urban atmosphere in China
    (München : European Geopyhsical Union, 2013) Wang, Z.B.; Hu, M.; Mogensen, D.; Yue, D.L.; Zheng, J.; Zhang, R.Y.; Liu, Y.; Yuan, B.; Li, X.; Shao, M.; Zhou, L.; Wu, Z.J.; Wiedensohler, A.; Boy, M.
    Simulations of sulfuric acid concentration and new particle formation are performed by using the zero-dimensional version of the model MALTE (Model to predict new Aerosol formation in the Lower TropospherE) and measurements from the Campaign of Air Quality Research in Beijing and Surrounding areas (CAREBeijing) in 2008. Chemical reactions from the Master Chemical Mechanism version 3.2 (MCM v3.2) are used in the model. High correlation (slope = 0.72, R = 0.74) between the modelled and observed sulfuric acid concentrations is found during daytime (06:00–18:00). The aerosol dynamics are simulated by the University of Helsinki Multicomponent Aerosol (UHMA) model including several nucleation mechanisms. The results indicate that the model is able to predict the on- and offset of new particle formation in an urban atmosphere in China. In addition, the number concentrations of newly formed particles in kinetic-type nucleation including homogenous homomolecular (J=K[H2SO4]2) and homogenous heteromolecular nucleation involving organic vapours (J=Khet[H2SO4][Org]) are in satisfactory agreement with the observations. However, the specific organic compounds that possibly participate in the nucleation process should be investigated in further studies. For the particle growth, only a small fraction of the oxidized total organics condense onto the particles in polluted environments. Meanwhile, the OH and O3 oxidation mechanism contribute 5.5% and 94.5% to the volume concentration of small particles, indicating the particle growth is more controlled by the precursor gases and their oxidation by O3.
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    Emittance Reduction of RF Photoinjector Generated Electron Beams by Transverse Laser Beam Shaping
    (Bristol : IOP Publ., 2019) Gross, M.; Qian, H.J.; Boonpornprasert, P.; Chen, Y.; Good, J.D.; Huck, H.; Isaev, I.; Koschitzki, C.; Krasilnikov, M.; Lal, S.; Li, X.; Lishilin, O.; Loisch, G.; Melkumyan, D.; Mohanty, S.K.; Niemczyk, R.; Oppelt, A.; Shaker, H.; Shu, G.; Stephan, F.; Vashchenko, G.; Will, I.
    Laser pulse shaping is one of the key elements to generate low emittance electron beams with RF photoinjectors. Ultimately high performance can be achieved with ellipsoidal laser pulses, but 3-dimensional shaping is challenging. High beam quality can also be reached by simple transverse pulse shaping, which has demonstrated improved beam emittance compared to a transversely uniform laser in the 'pancake' photoemission regime. In this contribution we present the truncation of a Gaussian laser at a radius of approximately one sigma in the intermediate (electron bunch length directly after emission about the same as radius) photoemission regime with high acceleration gradients (up to 60 MV/m). This type of electron bunch is used e.g. at the European XFEL and FLASH free electron lasers at DESY, Hamburg site and is being investigated in detail at the Photoinjector Test facility at DESY in Zeuthen (PITZ). Here we present ray-tracing simulations and experimental data of a laser beamline upgrade enabling variable transverse truncation. Initial projected emittance measurements taken with help of this setup are shown, as well as supporting beam dynamics simulations. Additional simulations show the potential for substantial reduction of slice emittance at PITZ. © Published under licence by IOP Publishing Ltd.
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    Characterization of self-modulated electron bunches in an argon plasma
    (Bristol : IOP Publ., 2018) Gross, M.; Lishilin, O.; Loisch, G.; Boonpornprasert, P.; Chen, Y.; Engel, J.; Good, J.; Huck, H.; Isaev, I.; Krasilnikov, M.; Li, X.; Niemczyk, R.; Oppelt, A.; Qian, H.; Renier, Y.; Stephan, F.; Zhao, Q.; Brinkmann, R.; Martinez de la Ossa, A.; Osterhoff, J.; Grüner, F.J.; Mehrling, T.; Schroeder, C.B.; Will, I.
    The self-modulation instability is fundamental for the plasma wakefield acceleration experiment of the AWAKE (Advanced Wakefield Experiment) collaboration at CERN where this effect is used to generate proton bunches for the resonant excitation of high acceleration fields. Utilizing the availability of flexible electron beam shaping together with excellent diagnostics including an RF deflector, a supporting experiment was set up at the electron accelerator PITZ (Photo Injector Test facility at DESY, Zeuthen site), given that the underlying physics is the same. After demonstrating the effect [1] the next goal is to investigate in detail the self-modulation of long (with respect to the plasma wavelength) electron beams. In this contribution we describe parameter studies on self-modulation of a long electron bunch in an argon plasma. The plasma was generated with a discharge cell with densities in the 1013 cm-3 to 1015 cm-3 range. The plasma density was deduced from the plasma wavelength as indicated by the self-modulation period. Parameter scans were conducted with variable plasma density and electron bunch focusing.
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    EuPRAXIA Conceptual Design Report
    (Berlin ; Heidelberg : Springer, 2020) Assmann, R. W.; Weikum, M. K.; Akhter, T.; Alesini, D.; Alexandrova, A. S.; Anania, M. P.; Andreev, N. E.; Andriyash, I.; Artioli, M.; Aschikhin, A.; Audet, T.; Jafarinia, F. J.; Jakobsson, O.; Jaroszynski, D. A.; Jaster-Merz, S.; Joshi, C.; Kaluza, M.; Kando, M.; Karger, O. S.; Karsch, S.; Khazanov, E.; Bacci, A.; Khikhlukha, D.; Kirchen, M.; Kirwan, G.; Kitégi, C.; Knetsch, A.; Kocon, D.; Koester, P.; Kononenko, O. S.; Korn, G.; Kostyukov, I.; Barna, I. F.; Kruchinin, K. O.; Labate, L.; Le Blanc, C.; Lechner, C.; Lee, P.; Leemans, W.; Lehrach, A.; Li, X.; Li, Y.; Libov, V.; Bartocci, S.; Lifschitz, A.; Lindstrøm, C. A.; Litvinenko, V.; Lu, W.; Lundh, O.; Maier, A. R.; Malka, V.; Manahan, G. G.; Mangles, S. P. D.; Marcelli, A.; Bayramian, A.; Marchetti, B.; Marcouillé, O.; Marocchino, A.; Marteau, F.; Martinez de la Ossa, A.; Martins, J. L.; Mason, P. D.; Massimo, F.; Mathieu, F.; Maynard, G.; Beaton, A.; Mazzotta, Z.; Mironov, S.; Molodozhentsev, A. Y.; Morante, S.; Mosnier, A.; Mostacci, A.; Müller, A. -S.; Murphy, C. D.; Najmudin, Z.; Nghiem, P. A. P.; Beck, A.; Nguyen, F.; Niknejadi, P.; Nutter, A.; Osterhoff, J.; Oumbarek Espinos, D.; Paillard, J. -L.; Papadopoulos, D. N.; Patrizi, B.; Pattathil, R.; Pellegrino, L.; Bellaveglia, M.; Petralia, A.; Petrillo, V.; Piersanti, L.; Pocsai, M. A.; Poder, K.; Pompili, R.; Pribyl, L.; Pugacheva, D.; Reagan, B. A.; Resta-Lopez, J.; Beluze, A.; Ricci, R.; Romeo, S.; Rossetti Conti, M.; Rossi, A. R.; Rossmanith, R.; Rotundo, U.; Roussel, E.; Sabbatini, L.; Santangelo, P.; Sarri, G.; Bernhard, A.; Schaper, L.; Scherkl, P.; Schramm, U.; Schroeder, C. B.; Scifo, J.; Serafini, L.; Sharma, G.; Sheng, Z. M.; Shpakov, V.; Siders, C. W.; Biagioni, A.; Silva, L. O.; Silva, T.; Simon, C.; Simon-Boisson, C.; Sinha, U.; Sistrunk, E.; Specka, A.; Spinka, T. M.; Stecchi, A.; Stella, A.; Bielawski, S.; Stellato, F.; Streeter, M. J. V.; Sutherland, A.; Svystun, E. N.; Symes, D.; Szwaj, C.; Tauscher, G. E.; Terzani, D.; Toci, G.; Tomassini, P.; Bisesto, F. G.; Torres, R.; Ullmann, D.; Vaccarezza, C.; Valléau, M.; Vannini, M.; Vannozzi, A.; Vescovi, S.; Vieira, J. M.; Villa, F.; Wahlström, C. -G.; Bonatto, A.; Walczak, R.; Walker, P. A.; Wang, K.; Welsch, A.; Welsch, C. P.; Weng, S. M.; Wiggins, S. M.; Wolfenden, J.; Xia, G.; Yabashi, M.; Boulton, L.; Zhang, H.; Zhao, Y.; Zhu, J.; Zigler, A.; Brandi, F.; Brinkmann, R.; Briquez, F.; Brottier, F.; Bründermann, E.; Büscher, M.; Buonomo, B.; Bussmann, M. H.; Bussolino, G.; Campana, P.; Cantarella, S.; Cassou, K.; Chancé, A.; Chen, M.; Chiadroni, E.; Cianchi, A.; Cioeta, F.; Clarke, J. A.; Cole, J. M.; Costa, G.; Couprie, M. -E.; Cowley, J.; Croia, M.; Cros, B.; Crump, P. A.; D’Arcy, R.; Dattoli, G.; Del Dotto, A.; Delerue, N.; Del Franco, M.; Delinikolas, P.; De Nicola, S.; Dias, J. M.; Di Giovenale, D.; Diomede, M.; Di Pasquale, E.; Di Pirro, G.; Di Raddo, G.; Dorda, U.; Erlandson, A. C.; Ertel, K.; Esposito, A.; Falcoz, F.; Falone, A.; Fedele, R.; Ferran Pousa, A.; Ferrario, M.; Filippi, F.; Fils, J.; Fiore, G.; Fiorito, R.; Fonseca, R. A.; Franzini, G.; Galimberti, M.; Gallo, A.; Galvin, T. C.; Ghaith, A.; Ghigo, A.; Giove, D.; Giribono, A.; Gizzi, L. A.; Grüner, F. J.; Habib, A. F.; Haefner, C.; Heinemann, T.; Helm, A.; Hidding, B.; Holzer, B. J.; Hooker, S. M.; Hosokai, T.; Hübner, M.; Ibison, M.; Incremona, S.; Irman, A.; Iungo, F.
    This report presents the conceptual design of a new European research infrastructure EuPRAXIA. The concept has been established over the last four years in a unique collaboration of 41 laboratories within a Horizon 2020 design study funded by the European Union. EuPRAXIA is the first European project that develops a dedicated particle accelerator research infrastructure based on novel plasma acceleration concepts and laser technology. It focuses on the development of electron accelerators and underlying technologies, their user communities, and the exploitation of existing accelerator infrastructures in Europe. EuPRAXIA has involved, amongst others, the international laser community and industry to build links and bridges with accelerator science — through realising synergies, identifying disruptive ideas, innovating, and fostering knowledge exchange. The Eu-PRAXIA project aims at the construction of an innovative electron accelerator using laser- and electron-beam-driven plasma wakefield acceleration that offers a significant reduction in size and possible savings in cost over current state-of-the-art radiofrequency-based accelerators. The foreseen electron energy range of one to five gigaelectronvolts (GeV) and its performance goals will enable versatile applications in various domains, e.g. as a compact free-electron laser (FEL), compact sources for medical imaging and positron generation, table-top test beams for particle detectors, as well as deeply penetrating X-ray and gamma-ray sources for material testing. EuPRAXIA is designed to be the required stepping stone to possible future plasma-based facilities, such as linear colliders at the high-energy physics (HEP) energy frontier. Consistent with a high-confidence approach, the project includes measures to retire risk by establishing scaled technology demonstrators. This report includes preliminary models for project implementation, cost and schedule that would allow operation of the full Eu-PRAXIA facility within 8—10 years.
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    A diuranium carbide cluster stabilized inside a C80 fullerene cage
    (London : Nature Publishing Group, 2018) Zhang, X.; Li, W.; Feng, L.; Chen, X.; Hansen, A.; Grimme, S.; Fortier, S.; Sergentu, D.-C.; Duignan, T.J.; Autschbach, J.; Wang, S.; Wang, Y.; Velkos, G.; Popov, A.A.; Aghdassi, N.; Duhm, S.; Li, X.; Li, J.; Echegoyen, L.; Schwarz, W.H.E.; Chen, N.
    Unsupported non-bridged uranium-carbon double bonds have long been sought after in actinide chemistry as fundamental synthetic targets in the study of actinide-ligand multiple bonding. Here we report that, utilizing I h(7)-C80 fullerenes as nanocontainers, a diuranium carbide cluster, U=C=U, has been encapsulated and stabilized in the form of UCU@I h(7)-C80. This endohedral fullerene was prepared utilizing the Krätschmer-Huffman arc discharge method, and was then co-crystallized with nickel(II) octaethylporphyrin (NiII-OEP) to produce UCU@I h(7)-C80·[NiII-OEP] as single crystals. X-ray diffraction analysis reveals a cage-stabilized, carbide-bridged, bent UCU cluster with unexpectedly short uranium-carbon distances (2.03 Å) indicative of covalent U=C double-bond character. The quantum-chemical results suggest that both U atoms in the UCU unit have formal oxidation state of +5. The structural features of UCU@I h(7)-C80 and the covalent nature of the U(f1)=C double bonds were further affirmed through various spectroscopic and theoretical analyses.
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    Assessing the influence of the Merzbacher Lake outburst floods on discharge using the hydrological model SWIM in the Aksu headwaters, Kyrgyzstan/NW China
    (Chichester : John Wiley and Sons Ltd, 2013) Wortmann, M.; Krysanova, V.; Kundzewicz, Z.W.; Su, B.; Li, X.
    Glacial lake outburst floods (GLOF) often have a significant impact on downstream users. Including their effects in hydrological models, identifying past occurrences and assessing their potential impacts are challenges for hydrologists working in mountainous catchments. The regularly outbursting Merzbacher Lake is located in the headwaters of the Aksu River, the most important source of water discharge to the Tarim River, northwest China. Modelling its water resources and the evaluation of potential climate change impacts on river discharge are indispensable for projecting future water availability for the intensively cultivated river oases downstream of the Merzbacher Lake and along the Tarim River. The semi-distributed hydrological model SWIM was calibrated to the outlet station Xiehela on the Kumarik River, by discharge the largest tributary to the Aksu River. The glacial lake outburst floods add to the difficulties of modelling this high-mountain, heavily glaciated catchment with poor data coverage and quality. The aims of the study are to investigate the glacier lake outburst floods using a modelling tool. Results include a two-step model calibration of the Kumarik catchment, an approach for the identification of the outburst floods using the measured gauge data and the modelling results and estimations of the outburst flood volumes. Results show that a catchment model can inform GLOF investigations by providing 'normal' (i.e. without the outburst floods) catchment discharge. The comparison of the simulated and observed discharge proves the occurrence of GLOFs and highlights the influences of the GLOFs on the downstream water balance.
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    The 2022 Plasma Roadmap: low temperature plasma science and technology
    (Bristol : IOP Publ., 2022) Adamovich, I.; Agarwal, S.; Ahedo, E.; Alves, L.L.; Baalrud, S.; Babaeva, N.; Bogaerts, A.; Bourdon, A.; Bruggeman, P.J.; Canal, C.; Choi, E.H.; Coulombe, S.; Donkó, Z.; Graves, D.B.; Hamaguchi, S.; Hegemann, D.; Hori, M.; Kim, H.-H.; Kroesen, G.M.W.; Kushner, M.J.; Laricchiuta, A.; Li, X.; Magin, T.E.; Mededovic Thagard, S.; Miller, V.; Murphy, A.B.; Oehrlein, G.S.; Puac, N.; Sankaran, R.M.; Samukawa, S.; Shiratani, M.; Šimek, M.; Tarasenko, N.; Terashima, K.; Thomas Jr, E.; Trieschmann, J.; Tsikata, S.; Turner, M.M.; Van Der Walt, I.J.; Van De Sanden, M.C.M.; Von Woedtke, T.
    The 2022 Roadmap is the next update in the series of Plasma Roadmaps published by Journal of Physics D with the intent to identify important outstanding challenges in the field of low-temperature plasma (LTP) physics and technology. The format of the Roadmap is the same as the previous Roadmaps representing the visions of 41 leading experts representing 21 countries and five continents in the various sub-fields of LTP science and technology. In recognition of the evolution in the field, several new topics have been introduced or given more prominence. These new topics and emphasis highlight increased interests in plasma-enabled additive manufacturing, soft materials, electrification of chemical conversions, plasma propulsion, extreme plasma regimes, plasmas in hypersonics, data-driven plasma science and technology and the contribution of LTP to combat COVID-19. In the last few decades, LTP science and technology has made a tremendously positive impact on our society. It is our hope that this roadmap will help continue this excellent track record over the next 5-10 years.