TY  - JOUR
A1  - Warren, Donald C.
A1  - Ellison, Donald C.
A1  - Barkov, Maxim V.
A1  - Nagataki, Shigehiro
T1  - Nonlinear Particle Acceleration and Thermal Particles in GRB Afterglows
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - The standard model for GRB afterglow emission treats the accelerated electron population as a simple power law, N(E) proportional to E-p for p greater than or similar to 2. However, in standard Fermi shock acceleration, a substantial fraction of the swept-up particles do not enter the acceleration process at all. Additionally, if acceleration is efficient, then the nonlinear back-reaction of accelerated particles on the shock structure modifies the shape of the nonthermal tail of the particle spectra. Both of these modifications to the standard synchrotron afterglow impact the luminosity, spectra, and temporal variation of the afterglow. To examine the effects of including thermal particles and nonlinear particle acceleration on afterglow emission, we follow a hydrodynamical model for an afterglow jet and simulate acceleration at numerous points during the evolution. When thermal particles are included, we find that the electron population is at no time well fitted by a single power law, though the highest-energy electrons are; if the acceleration is efficient, then the power-law region is even smaller. Our model predicts hard-soft-hard spectral evolution at X-ray energies, as well as an uncoupled X-ray and optical light curve. Additionally, we show that including emission from thermal particles has drastic effects (increases by factors of 100 and 30, respectively) on the observed flux at optical and GeV energies. This enhancement of GeV emission makes afterglow detections by future gamma-ray observatories, such as CTA, very likely.
KW  - acceleration of particles
KW  - cosmic rays
KW  - gamma-ray burst: general
KW  - shock waves
KW  - turbulence
Y1  - 2017
U6  - https://doi.org/10.3847/1538-4357/aa56c3
SN  - 0004-637X
SN  - 1538-4357
VL  - 835
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Almeida, Leonardo A.
A1  - Sana, H.
A1  - Taylor, W.
A1  - Barbá, Rodolfo
A1  - Bonanos, Alceste Z.
A1  - Crowther, Paul
A1  - Damineli, Augusto
A1  - de Koter, A.
A1  - de Mink, Selma E.
A1  - Evans, C. J.
A1  - Gieles, Mark
A1  - Grin, Nathan J.
A1  - Hénault-Brunet, V.
A1  - Langer, Norbert
A1  - Lennon, D.
A1  - Lockwood, Sean
A1  - Maíz Apellániz, Jesús
A1  - Moffat, A. F. J.
A1  - Neijssel, C.
A1  - Norman, C.
A1  - Ramírez-Agudelo, O. H.
A1  - Richardson, N. D.
A1  - Schootemeijer, Abel
A1  - Shenar, Tomer
A1  - Soszyński, Igor
A1  - Tramper, Frank
A1  - Vink, J. S.
T1  - The tarantula massive binary monitoring
BT  - I. Observational campaign and OB-type spectroscopic binaries
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context:
Massive binaries play a crucial role in the Universe. Knowing the distributions of their orbital parameters is important for a wide range of topics from stellar feedback to binary evolution channels and from the distribution of supernova types to gravitational wave progenitors, yet no direct measurements exist outside the Milky Way.
Aims:
The Tarantula Massive Binary Monitoring project was designed to help fill this gap by obtaining multi-epoch radial velocity (RV) monitoring of 102 massive binaries in the 30 Doradus region.
Methods: 
In this paper we analyze 32 FLAMES/GIRAFFE observations of 93 O- and 7 B-type binaries. We performed a Fourier analysis and obtained orbital solutions for 82 systems: 51 single-lined (SB1) and 31 double-lined (SB2) spectroscopic binaries.
Results: 
Overall, the binary fraction and orbital properties across the 30 Doradus region are found to be similar to existing Galactic samples. This indicates that within these domains environmental effects are of second order in shaping the properties of massive binary systems. A small difference is found in the distribution of orbital periods, which is slightly flatter (in log space) in 30 Doradus than in the Galaxy, although this may be compatible within error estimates and differences in the fitting methodology. Also, orbital periods in 30 Doradus can be as short as 1.1 d, somewhat shorter than seen in Galactic samples. Equal mass binaries (q> 0.95) in 30 Doradus are all found outside NGC 2070, the central association that surrounds R136a, the very young and massive cluster at 30 Doradus’s core. Most of the differences, albeit small, are compatible with expectations from binary evolution. One outstanding exception, however, is the fact that earlier spectral types (O2–O7) tend to have shorter orbital periods than later spectral types (O9.2–O9.7).
Conclusions: 
Our results point to a relative universality of the incidence rate of massive binaries and their orbital properties in the metallicity range from solar (Z⊙) to about half solar. This provides the first direct constraints on massive binary properties in massive star-forming galaxies at the Universe’s peak of star formation at redshifts z ~ 1 to 2 which are estimated to have Z ~ 0.5 Z⊙.
KW  - stars: early-type
KW  - stars: massive
KW  - binaries: spectroscopic
KW  - binaries: close
Y1  - 2017
U6  - https://doi.org/10.1051/0004-6361/201629844
SN  - 1432-0746
VL  - 598
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Gorobtsov, O. Yu.
A1  - Mercurio, G.
A1  - Brenner, G.
A1  - Lorenz, Ulf
A1  - Gerasimova, N.
A1  - Kurta, R. P.
A1  - Hieke, F.
A1  - Skopintsev, P.
A1  - Zaluzhnyy, I.
A1  - Lazarev, S.
A1  - Dzhigaev, D.
A1  - Rose, M.
A1  - Singer, A.
A1  - Wurth, W.
A1  - Vartanyants, I. A.
T1  - Statistical properties of a free-electron laser revealed by Hanbury Brown-Twiss interferometry
JF  - Physical review : A, Atomic, molecular, and optical physics
N2  - We present a comprehensive experimental analysis of statistical properties of the self-amplified spontaneous emission free-electron laser (FEL) FLASH by means of Hanbury Brown and Twiss interferometry. The experiments were performed at FEL wavelengths of 5.5, 13.4, and 20.8 nm. We determined the second-order intensity correlation function for all wavelengths and different operation conditions of FLASH. In all experiments a high degree of spatial coherence (above 50%) was obtained. Our analysis performed in spatial and spectral domains provided us with the independent measurements of an average pulse duration of the FEL that were below 60 fs. To explain the complicated behavior of the second-order intensity correlation function we developed an advanced theoretical model that includes the presence of multiple beams and external positional jitter of the FEL pulses. By this analysis we determined that in one of the experiments external positional jitter was about 25% of the beam size. We envision that methods developed in our study will be used widely for analysis and diagnostics of FEL radiation.
Y1  - 2017
U6  - https://doi.org/10.1103/PhysRevA.95.023843
SN  - 2469-9926
SN  - 2469-9934
VL  - 95
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Godec, Aljaž
A1  - Metzler, Ralf
T1  - First passage time statistics for two-channel diffusion
JF  - Journal of physics : A, Mathematical and theoretical
N2  - We present rigorous results for the mean first passage time and first passage time statistics for two-channel Markov additive diffusion in a 3-dimensional spherical domain. Inspired by biophysical examples we assume that the particle can only recognise the target in one of the modes, which is shown to effect a non-trivial first passage behaviour. We also address the scenario of intermittent immobilisation. In both cases we prove that despite the perfectly non-recurrent motion of two-channel Markov additive diffusion in 3 dimensions the first passage statistics at long times do not display Poisson-like behaviour if none of the phases has a vanishing diffusion coefficient. This stands in stark contrast to the standard (one-channel) Markov diffusion counterpart. We also discuss the relevance of our results in the context of cellular signalling.
KW  - first passage time
KW  - Markov additive processes
KW  - Fokker-Planck equation
KW  - random search processes
KW  - coupled initial boundary value problem
KW  - cellular signalling
KW  - asymptotic analysis
Y1  - 2017
U6  - https://doi.org/10.1088/1751-8121/aa5204
SN  - 1751-8113
SN  - 1751-8121
VL  - 50
IS  - 8
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Goychuk, Igor
T1  - Quantum ergodicity breaking in semi-classical electron transfer dynamics
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - Can the statistical properties of single-electron transfer events be correctly predicted within a common equilibrium ensemble description? This fundamental in nanoworld question of ergodic behavior is scrutinized within a very basic semi-classical curve-crossing problem. It is shown that in the limit of non-adiabatic electron transfer (weak tunneling) well-described by the Marcus-Levich-Dogonadze (MLD) rate the answer is yes. However, in the limit of the so-called solvent-controlled adiabatic electron transfer, a profound breaking of ergodicity occurs. Namely, a common description based on the ensemble reduced density matrix with an initial equilibrium distribution of the reaction coordinate is not able to reproduce the statistics of single-trajectory events in this seemingly classical regime. For sufficiently large activation barriers, the ensemble survival probability in a state remains nearly exponential with the inverse rate given by the sum of the adiabatic curve crossing (Kramers) time and the inverse MLD rate. In contrast, near to the adiabatic regime, the single-electron survival probability is clearly non-exponential, even though it possesses an exponential tail which agrees well with the ensemble description. Initially, it is well described by a Mittag-Leffler distribution with a fractional rate. Paradoxically, the mean transfer time in this classical on the ensemble level regime is well described by the inverse of the nonadiabatic quantum tunneling rate on a single particle level. An analytical theory is developed which perfectly agrees with stochastic simulations and explains our findings.
Y1  - 2016
U6  - https://doi.org/10.1039/c6cp07206b
SN  - 1463-9076
SN  - 1463-9084
VL  - 19
SP  - 3056
EP  - 3066
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Kunnus, Kristjan
A1  - Josefsson, I.
A1  - Schreck, Simon Frederik
A1  - Quevedo, W.
A1  - Miedema, P. S.
A1  - Techert, S.
A1  - de Groot, F. M. F.
A1  - Föhlisch, Alexander
A1  - Odelius, M.
A1  - Wernet, Ph.
T1  - Quantifying covalent interactions with resonant inelastic soft X-ray scattering
BT  - case study of Ni2+ aqua complex
JF  - Chemical physics letters
N2  - We analyze the effects of covalent interactions in Ni 2p3d resonant inelastic X-ray scattering (RIXS) spectra from aqueous Ni2+ ions and find that the relative RIXS intensities of ligand-to-metal charge-transfer final states with respect to the ligand-field final states reflect the covalent mixing between Ni 3d and water orbitals. Specifically, the experimental intensity ratio at the Ni L-3-edge allows to determine that the Ni 3d orbitals have on average 5.5% of water character. We propose that 2p3d RIXS at the Ni L-3-edge can be utilized to quantify covalency in Ni complexes without the use of external references or simulations.
KW  - Transition-metal ion
KW  - Aqueous solution
KW  - Covalent interaction
KW  - Resonant inelastic X-ray scattering
KW  - Ligand-field state
KW  - Charge-transfer state
Y1  - 2016
U6  - https://doi.org/10.1016/j.cplett.2016.12.046
SN  - 0009-2614
SN  - 1873-4448
VL  - 669
SP  - 196
EP  - 201
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Husemann, Bernd
A1  - Bielby, R.
A1  - Jahnke, K.
A1  - Arrigoni-Battaia, F.
A1  - Worseck, Gabor
A1  - Shanks, T.
A1  - Wardlow, J.
A1  - Scholtz, J.
T1  - Cosmic dance at z similar to 3
BT  - Detecting the host galaxies of the dual AGN system LBQS 0302-0019 and Jil with HAWK-I plus GRAAL
JF  - Astronomy and astrophysics : an international weekly journal
N2  - We recently discovered that the luminous radio-quiet (QSO) LBQS 0302-0019 at z=3.286 is likely accompanied by an obscured AGN at 20 kpc projected distance, which we dubbed Jil. It represents the tightest candidate obscured/unobscured dual AGN system at z >3. To verify the dual AGN scenario we obtained deep K-s band (rest-frame V band) imaging with the VLT/HAWK-I+GRAAL instrument at 0 '.4 resolution during science verification in January 2018. Indeed, we detect the individual host galaxies of the QSO and Jil with estimated stellar masses of log(M-*/M-circle dot)=11.4 +/- 0.5 and log(M-*/M-circle dot)=10.9 +/- 0.5, respectively. Near-IR spectra obtained with VLT-KMOS reveal a clear [O-III] lambda 5007 line detection at the location of Jil which does not contribute significantly to the Ks band flux. Both observations therefore corroborate the dual AGN scenario. A comparison to Illustris cosmological simulations suggests a parent halo mass of log(M-halo/M-*)=13.2 +/- 0.5 for this interacting galaxy system, corresponding to a very massive dark matter halo at that epoch.
KW  - Galaxies: interactions
KW  - Galaxies: high-redshift
KW  - large-scale structure of Universe
KW  - instrumentation: adaptive optics
KW  - quasars: individual: LBQS 0302-0018
Y1  - 2018
U6  - https://doi.org/10.1051/0004-6361/201833363
SN  - 1432-0746
VL  - 614
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Sanchez-Ayaso, María de la Estrella
A1  - del Valle, Maria Victoria
A1  - Marti, Josep
A1  - Romero, G. E.
A1  - Luque-Escamilla, Pedro Luis
T1  - Possible association of two Stellar Bowshocks with Unidentified Fermi Sources
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - The bowshocks of runaway stars had been theoretically proposed as gamma-ray sources. However, this hypothesis has not been confirmed by observations to date. In this paper, we present two runaway stars (lambda Cep and LS 2355) whose bowshocks are coincident with the unidentified Fermi gamma-ray sources 3FLG J2210.1+5925 and 3FGL J1128.7-6232, respectively. After performing a cross-correlation between different catalogs at distinct wavelengths, we found that these bowshocks are the most peculiar objects in the Fermi position ellipses. Then we computed the inverse Compton emission and fitted the Fermi data in order to test the viability of both runaway stars as potential counterparts of the two high-energy sources. We obtained very reasonable values for the fitted parameters of both stars. We also evaluated the possibility for the source 3FGL J1128.7-6232, which is positionally coincident with a H II region, to be the result of background cosmic-ray protons interacting with the matter of the cloud, as well as the probability of a pure chance association. We conclude that the gamma rays from these Fermi sources might be produced in the bowshocks of the considered runaway stars. In such a case, these would be the first sources of this class ever detected at gamma rays.
KW  - stars: winds, outflows
Y1  - 2018
U6  - https://doi.org/10.3847/1538-4357/aac7c7
SN  - 0004-637X
SN  - 1538-4357
VL  - 861
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Kegeles, Alexander
A1  - Oriti, Daniele
A1  - Tomlin, Casey
T1  - Inequivalent coherent state representations in group field theory
JF  - Classical and quantum gravit
N2  - In this paper we propose an algebraic formulation of group field theory and consider non-Fock representations based on coherent states. We show that we can construct representations with an infinite number of degrees of freedom on compact manifolds. We also show that these representations break translation symmetry. Since such representations can be regarded as quantum gravitational systems with an infinite number of fundamental pre-geometric building blocks, they may be more suitable for the description of effective geometrical phases of the theory.
KW  - group field theory
KW  - quantum gravity
KW  - quantum field theory
KW  - spin foam models
Y1  - 2018
U6  - https://doi.org/10.1088/1361-6382/aac39f
SN  - 0264-9381
SN  - 1361-6382
VL  - 35
IS  - 12
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Quade, Markus
A1  - Abel, Markus
A1  - Kutz, J. Nathan
A1  - Brunton, Steven L.
T1  - Sparse identification of nonlinear dynamics for rapid model recovery
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - Big data have become a critically enabling component of emerging mathematical methods aimed at the automated discovery of dynamical systems, where first principles modeling may be intractable. However, in many engineering systems, abrupt changes must be rapidly characterized based on limited, incomplete, and noisy data. Many leading automated learning techniques rely on unrealistically large data sets, and it is unclear how to leverage prior knowledge effectively to re-identify a model after an abrupt change. In this work, we propose a conceptual framework to recover parsimonious models of a system in response to abrupt changes in the low-data limit. First, the abrupt change is detected by comparing the estimated Lyapunov time of the data with the model prediction. Next, we apply the sparse identification of nonlinear dynamics (SINDy) regression to update a previously identified model with the fewest changes, either by addition, deletion, or modification of existing model terms. We demonstrate this sparse model recovery on several examples for abrupt system change detection in periodic and chaotic dynamical systems. Our examples show that sparse updates to a previously identified model perform better with less data, have lower runtime complexity, and are less sensitive to noise than identifying an entirely new model. The proposed abrupt-SINDy architecture provides a new paradigm for the rapid and efficient recovery of a system model after abrupt changes.
Y1  - 2018
U6  - https://doi.org/10.1063/1.5027470
SN  - 1054-1500
SN  - 1089-7682
VL  - 28
IS  - 6
PB  - American Institute of Physics
CY  - Melville
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  - Estrada, Ernesto
A1  - Delvenne, Jean-Charles
A1  - Hatano, Naomichi
A1  - Mateos, Jose L.
A1  - Metzler, Ralf
A1  - Riascos, Alejandro P.
A1  - Schaub, Michael T.
T1  - Random multi-hopper model
BT  - super-fast random walks on graphs
JF  - Journal of Complex Networks
N2  - We develop a mathematical model considering a random walker with long-range hops on arbitrary graphs. The random multi-hopper can jump to any node of the graph from an initial position, with a probability that decays as a function of the shortest-path distance between the two nodes in the graph. We consider here two decaying functions in the form of Laplace and Mellin transforms of the shortest-path distances. We prove that when the parameters of these transforms approach zero asymptotically, the hitting time in the multi-hopper approaches the minimum possible value for a normal random walker. We show by computational experiments that the multi-hopper explores a graph with clusters or skewed degree distributions more efficiently than a normal random walker. We provide computational evidences of the advantages of the random multi-hopper model with respect to the normal random walk by studying deterministic, random and real-world networks.
Y1  - 2018
U6  - https://doi.org/10.1093/comnet/cnx043
SN  - 2051-1310
SN  - 2051-1329
VL  - 6
IS  - 3
SP  - 382
EP  - 403
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Wetterich, Sebastian
A1  - Schirrmeiste, Lutz
A1  - Nazarova, Larisa B.
A1  - Palagushkina, Olga
A1  - Bobrov, Anatoly
A1  - Pogosyan, Lilit
A1  - Savelieva, Larisa
A1  - Syrykh, Liudmila
A1  - Matthes, Heidrun
A1  - Fritz, Michael
A1  - Günther, Frank
A1  - Opel, Thomas
A1  - Meyer, Hanno
T1  - Holocene thermokarst and pingo development in the Kolyma Lowland (NE Siberia)
JF  - Permafrost and Periglacial Processes
N2  - Ground ice and sedimentary records of a pingo exposure reveal insights into Holocene permafrost, landscape and climate dynamics. Early to mid-Holocene thermokarst lake deposits contain rich floral and faunal paleoassemblages, which indicate lake shrinkage and decreasing summer temperatures (chironomid-based T-July) from 10.5 to 3.5 cal kyr BP with the warmest period between 10.5 and 8 cal kyr BP. Talik refreezing and pingo growth started about 3.5 cal kyr BP after disappearance of the lake. The isotopic composition of the pingo ice (delta O-18 - 17.1 +/- 0.6 parts per thousand, delta D -144.5 +/- 3.4 parts per thousand, slope 5.85, deuterium excess -7.7 +/- 1.5 parts per thousand) point to the initial stage of closed-system freezing captured in the record. A differing isotopic composition within the massive ice body was found (delta O-18 - 21.3 +/- 1.4 parts per thousand, delta D -165 +/- 11.5 parts per thousand, slope 8.13, deuterium excess 4.9 +/- 3.2 parts per thousand), probably related to the infill of dilation cracks by surface water with quasi-meteoric signature. Currently inactive syngenetic ice wedges formed in the thermokarst basin after lake drainage. The pingo preserves traces of permafrost response to climate variations in terms of ground-ice degradation (thermokarst) during the early and mid-Holocene, and aggradation (wedge-ice and pingo-ice growth) during the late Holocene.
KW  - bioindicators
KW  - cryolithology
KW  - hydrochemistry
KW  - Khalerchinskaya tundra
KW  - stable water isotopes
Y1  - 2018
U6  - https://doi.org/10.1002/ppp.1979
SN  - 1045-6740
SN  - 1099-1530
VL  - 29
IS  - 3
SP  - 182
EP  - 198
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Keles, Engin
T1  - Spectral signature of atmospheric winds in high-resolution transit observations
JF  - Monthly Notices of the Royal Astronomical Society
N2  - The study of exoplanet atmospheres showed large diversity compared to the planets in our Solar system. Especially Jupiter-type exoplanets orbiting their host star in close orbits, the so-called hot and ultra-hot Jupiters, have been studied in detail due to their enhanced atmospheric signature. Due to their tidally locked status, the temperature difference between the day- and nightside triggers atmospheric winds that can lead to various fingerprints in the observations. Spatially resolved absorption lines during transit such as sodium (Na) could be a good tracer for such winds. Different works resolved the Na absorption lines on different exoplanets which show different line widths. Assuming that this could be attributed to such zonal jet streams, this work models the effect of such winds on synthetic absorption lines. For this, transiting Jupiter-type planets with rotational velocities similar to hot and ultra-hot Jupiter are considered. The investigation shows that high wind velocities could reproduce the broadening of Na-line profiles inferred in different high-resolution transit observations. There is a tendency that the broadening values decrease for planets with lower equilibrium temperature. This could be explained by atmospheric drag induced by the ionization of alkali lines that slow down the zonal jet streams, favouring their existence on hot Jupiter rather than ultra-hot Jupiter.
Y1  - 2021
U6  - https://doi.org/10.1093/mnras/stab099
VL  - 502
IS  - 1
SP  - 1456
EP  - 1468
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Holzmeier, Fabian
A1  - Wolf, Thomas J. A.
A1  - Gienger, Christian
A1  - Wagner, Isabella
A1  - Bozek, J.
A1  - Nandi, S.
A1  - Nicolas, C.
A1  - Fischer, Ingo
A1  - Gühr, Markus
A1  - Fink, Reinhold F.
T1  - Normal and resonant Auger spectroscopy of isocyanic acid, HNCO
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - In this paper, we investigate HNCO by resonant and nonresonant Auger electron spectroscopy at the K-edges of carbon, nitrogen, and oxygen, employing soft X-ray synchrotron radiation. In comparison with the isosteric but linear CO2 molecule, spectra of the bent HNCO molecule are similar but more complex due to its reduced symmetry, wherein the degeneracy of the π-orbitals is lifted. Resonant Auger electron spectra are presented at different photon energies over the first core-excited 1s → 10a′ resonance. All Auger electron spectra are assigned based on ab initio configuration interaction computations combined with the one-center approximation for Auger intensities and moment theory to consider vibrational motion. The calculated spectra were scaled by a newly introduced energy scaling factor, and generally, good agreement is found between experiment and theory for normal as well as resonant Auger electron spectra. A comparison of resonant Auger spectra with nonresonant Auger structures shows a slight broadening as well as a shift of the former spectra between −8 and −9 eV due to the spectating electron. Since HNCO is a small molecule and contains the four most abundant atoms of organic molecules, the reported Auger electron decay spectra will provide a benchmark for further theoretical approaches in the computation of core electron spectra.
Y1  - 2018
U6  - https://doi.org/10.1063/1.5030621
SN  - 0021-9606
SN  - 1089-7690
VL  - 149
IS  - 3
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Grätz, Fabio M.
A1  - Seiss, Martin
A1  - Spahn, Frank
T1  - Formation of moon-induced gaps in dense planetary rings
BT  - application to the rings of saturn
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We develop an axisymmetric diffusion model to describe radial density profiles in the vicinity of tiny moons embedded in planetary rings. Our diffusion model accounts for the gravitational scattering of the ring particles by an embedded moon and for the viscous diffusion of the ring matter back into the gap. With test particle simulations, we show that the scattering of the ring particles passing the moon is larger for small impact parameters than estimated by Goldreich & Tremaine and Namouni. This is significant for modeling the Keeler gap. We apply our model to the gaps of the moons Pan and Daphnis embedded in the outer A ring of Saturn with the aim to estimate the shear viscosity of the ring in the vicinity of the Encke and Keeler gap. In addition, we analyze whether tiny icy moons whose dimensions lie below Cassini's resolution capabilities would be able to explain the gap structure of the C ring and the Cassini division.
KW  - diffusion
KW  - planets and satellites: rings
KW  - scattering
Y1  - 2018
U6  - https://doi.org/10.3847/1538-4357/aace00
SN  - 0004-637X
SN  - 1538-4357
VL  - 862
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - He, Yongli
A1  - Huang, Jianping
A1  - Li, Dongdong
A1  - Xie, Yongkun
A1  - Zhang, Guolong
A1  - Qi, Yulei
A1  - Wang, Shanshan
A1  - Totz, Sonja Juliana
T1  - Comparison of the effect of land-sea thermal contrast on interdecadal variations in winter and summer blockings
JF  - Climate dynamics : observational, theoretical and computational research on the climate system
N2  - The influence of winter and summer land-sea surface thermal contrast on blocking for 1948-2013 is investigated using observations and the coupled model intercomparison project outputs. The land-sea index (LSI) is defined to measure the changes of zonal asymmetric thermal forcing under global warming. The summer LSI shows a slower increasing trend than winter during this period. For the positive of summer LSI, the EP flux convergence induced by the land-sea thermal forcing in the high latitude becomes weaker than normal, which induces positive anomaly of zonal-mean westerly and double-jet structure. Based on the quasiresonance amplification mechanism, the narrow and reduced westerly tunnel between two jet centers provides a favor environment for more frequent blocking. Composite analysis demonstrates that summer blocking shows an increasing trend of event numbers and a decreasing trend of durations. The numbers of the short-lived blocking persisting for 5-9 days significantly increases and the numbers of the long-lived blocking persisting for longer than 10 days has a weak increase than that in negative phase of summer LSI. The increasing transient wave activities induced by summer LSI is responsible for the decreasing duration of blockings. The increasing blocking due to summer LSI can further strengthen the continent warming and increase the summer LSI, which forms a positive feedback. The opposite dynamical effect of LSI on summer and winter blocking are discussed and found that the LSI-blocking negative feedback partially reduces the influence of the above positive feedback and induce the weak summer warming rate.
KW  - Land-sea thermal contrast
KW  - Blocking
KW  - Asymmetric warming
KW  - Double-jet
Y1  - 2017
U6  - https://doi.org/10.1007/s00382-017-3954-9
SN  - 0930-7575
SN  - 1432-0894
VL  - 51
IS  - 4
SP  - 1275
EP  - 1294
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Leitner, T.
A1  - Josefsson, Ida
A1  - Mazza, T.
A1  - Miedema, Piter S.
A1  - Schröder, H.
A1  - Beye, Martin
A1  - Kunnus, Kristjan
A1  - Schreck, S.
A1  - Düsterer, Stefan
A1  - Föhlisch, Alexander
A1  - Meyer, M.
A1  - Odelius, Michael
A1  - Wernet, Philippe
T1  - Time-resolved electron spectroscopy for chemical analysis of photodissociation
BT  - Photoelectron spectra of Fe(CO)(5), Fe(CO)(4), and Fe(CO)(3)
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - The prototypical photoinduced dissociation of Fe(CO)(5) in the gas phase is used to test time-resolved x-ray photoelectron spectroscopy for studying photochemical reactions. Upon one-photon excitation at 266 nm, Fe(CO)(5) successively dissociates to Fe(CO)(4) and Fe(CO)(3) along a pathway where both fragments retain the singlet multiplicity of Fe(CO)(5). The x-ray free-electron laser FLASH is used to probe the reaction intermediates Fe(CO)(4) and Fe(CO)(3) with time-resolved valence and core-level photoelectron spectroscopy, and experimental results are interpreted with ab initio quantum chemical calculations. Changes in the valence photoelectron spectra are shown to reflect changes in the valenceorbital interactions upon Fe-CO dissociation, thereby validating fundamental theoretical concepts in Fe-CO bonding. Chemical shifts of CO 3 sigma inner-valence and Fe 3 sigma core-level binding energies are shown to correlate with changes in the coordination number of the Fe center. We interpret this with coordination-dependent charge localization and core-hole screening based on calculated changes in electron densities upon core-hole creation in the final ionic states. This extends the established capabilities of steady-state electron spectroscopy for chemical analysis to time-resolved investigations. It could also serve as a benchmark for howcharge and spin density changes in molecular dissociation and excited-state dynamics are expressed in valence and core-level photoelectron spectroscopy. Published by AIP Publishing.
Y1  - 2018
U6  - https://doi.org/10.1063/1.5035149
SN  - 0021-9606
SN  - 1089-7690
VL  - 149
IS  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Olson, R.
A1  - An, Soon-Il
A1  - Fan, Y.
A1  - Evans, J. P.
A1  - Caesar, Levke
T1  - North Atlantic observations sharpen meridional overturning projections
JF  - Climate dynamics : observational, theoretical and computational research on the climate system
N2  - Atlantic Meridional Overturning Circulation (AMOC) projections are uncertain due to both model errors, as well as internal climate variability. An AMOC slowdown projected by many climate models is likely to have considerable effects on many aspects of global and North Atlantic climate. Previous studies to make probabilistic AMOC projections have broken new ground. However, they do not drift-correct or cross-validate the projections, and do not fully account for internal variability. Furthermore, they consider a limited subset of models, and ignore the skill of models at representing the temporal North Atlantic dynamics. We improve on previous work by applying Bayesian Model Averaging to weight 13 Coupled Model Intercomparison Project phase 5 models by their skill at modeling the AMOC strength, and its temporal dynamics, as approximated by the northern North-Atlantic temperature-based AMOC Index. We make drift-corrected projections accounting for structural model errors, and for the internal variability. Cross-validation experiments give approximately correct empirical coverage probabilities, which validates our method. Our results present more evidence that AMOC likely already started slowing down. While weighting considerably moderates and sharpens our projections, our results are at low end of previously published estimates. We project mean AMOC changes between periods 1960-1999 and 2060-2099 of -4.0 Sv and -6.8 Sv for RCP4.5 and RCP8.5 emissions scenarios respectively. The corresponding average 90% credible intervals for our weighted experiments are [-7.2, -1.2] and [-10.5, -3.7] Sv respectively for the two scenarios.
KW  - Atlantic Meridional Overturning Circulation
KW  - Climate modeling
KW  - Bayesian Model Averaging
KW  - Model structural error
KW  - Probabilistic projections
Y1  - 2017
U6  - https://doi.org/10.1007/s00382-017-3867-7
SN  - 0930-7575
SN  - 1432-0894
VL  - 50
IS  - 11-12
SP  - 4171
EP  - 4188
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Muzahid, S.
A1  - Fonseca, G.
A1  - Roberts, A.
A1  - Rosenwasser, B.
A1  - Richter, Philipp
A1  - Narayanan, A.
A1  - Churchill, C.
A1  - Charlton, J.
T1  - COS-Weak: probing the CGM using analogues of weak Mg II absorbers at z < 0.3
JF  - Monthly notices of the Royal Astronomical Society
N2  - We present a sample of 34 weak metal line absorbers at z < 0.3 selected by the simultaneous >3σ detections of the Si iiλ1260 and C iiλ1334 absorption lines, with Wr(SiII)<0.2 Å and Wr(CII)<0.3 Å, in archival HST/COS spectra. Our sample increases the number of known low-z ‘weak absorbers’ by a factor of >5. The column densities of H i and low-ionization metal lines obtained from Voigt profile fitting are used to build simple photoionization models. The inferred densities and line-of-sight thicknesses of the absorbers are in the ranges of −3.3 < log nH/cm−3 < −2.4 and ∼1 pc–50 kpc (median ≈500 pc), respectively. Most importantly, 85 per cent (50 per cent) of these absorbers show a metallicity of [Si/H]>−1.0(0.0)⁠. The fraction of systems showing near-/supersolar metallicity in our sample is significantly higher than in the H i-selected sample of Wotta et al., and the galaxy-selected sample of Prochaska et al., of absorbers probing the circum-galactic medium at similar redshift. A search for galaxies has revealed a significant galaxy-overdensity around these weak absorbers compared to random positions with a median impact parameter of 166 kpc from the nearest galaxy. Moreover, we find the presence of multiple galaxies in ≈80 per cent of the cases, suggesting group environments. The observed dN/dz of 0.8 ± 0.2 indicates that such metal-enriched, compact, dense structures are ubiquitous in the haloes of low-z group galaxies. We suggest that these are transient structures that are related to galactic outflows and/or stripping of metal-rich gas from galaxies.
KW  - galaxies: formation
KW  - galaxies: haloes
KW  - quasar: absorption line
Y1  - 2018
U6  - https://doi.org/10.1093/mnras/sty529
SN  - 0035-8711
SN  - 1365-2966
VL  - 476
IS  - 4
SP  - 4965
EP  - 4986
PB  - Oxford Univ. Press
CY  - Oxford
ER  -