TY  - JOUR
A1  - Mattern, M.
A1  - Pudell, Jan-Etienne
A1  - Laskin, G.
A1  - von Reppert, A.
A1  - Bargheer, Matias
T1  - Analysis of the temperature- and fluence-dependent magnetic stress in laser-excited SrRuO3
JF  - Structural Dynamics
N2  - We use ultrafast x-ray diffraction to investigate the effect of expansive phononic and contractive magnetic stress driving the picosecond strain response of a metallic perovskite SrRuO3 thin film upon femtosecond laser excitation. We exemplify how the anisotropic bulk equilibrium thermal expansion can be used to predict the response of the thin film to ultrafast deposition of energy. It is key to consider that the laterally homogeneous laser excitation changes the strain response compared to the near-equilibrium thermal expansion because the balanced in-plane stresses suppress the Poisson stress on the picosecond timescale. We find a very large negative Grüneisen constant describing the large contractive stress imposed by a small amount of energy in the spin system. The temperature and fluence dependence of the strain response for a double-pulse excitation scheme demonstrates the saturation of the magnetic stress in the high-fluence regime.
KW  - Thin films
KW  - Thermodynamic properties
KW  - Bragg peak
KW  - Ultrafast X-ray diffraction
KW  - Thermal effects
KW  - Phonons
KW  - Magnetism
KW  - Lattice dynamics
KW  - Lasers
KW  - Perovskites
Y1  - 2020
U6  - https://doi.org/10.1063/4.0000072
SN  - 2329-7778
ER  - 
TY  - JOUR
A1  - Reese, Ronja
A1  - Winkelmann, Hilke Ricarda
A1  - Gudmundsson, Gudmundur Hilmar
T1  - Grounding-line flux formula applied as a flux condition in numerical simulations fails for buttressed Antarctic ice streams
JF  - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union
N2  - Currently, several large-scale ice-flow models impose a condition on ice flux across grounding lines using an analytically motivated parameterisation of grounding-line flux. It has been suggested that employing this analytical expression alleviates the need for highly resolved computational domains around grounding lines of marine ice sheets. While the analytical flux formula is expected to be accurate in an unbuttressed flow-line setting, its validity has hitherto not been assessed for complex and realistic geometries such as those of the Antarctic Ice Sheet. Here the accuracy of this analytical flux formula is tested against an optimised ice flow model that uses a highly resolved computational mesh around the Antarctic grounding lines. We find that when applied to the Antarctic Ice Sheet the analytical expression provides inaccurate estimates of ice fluxes for almost all grounding lines. Furthermore, in many instances direct application of the analytical formula gives rise to unphysical complex-valued ice fluxes. We conclude that grounding lines of the Antarctic Ice Sheet are, in general, too highly buttressed for the analytical parameterisation to be of practical value for the calculation of grounding-line fluxes.
Y1  - 2018
U6  - https://doi.org/10.5194/tc-12-3229-2018
SN  - 1994-0416
SN  - 1994-0424
VL  - 12
IS  - 10
SP  - 3229
EP  - 3242
PB  - Copernicus
CY  - Göttingen
ER  - 
TY  - JOUR
A1  - Seiß, Martin
A1  - Albers, Nicole
A1  - Sremčević, Miodrag
A1  - Schmidt, Jürgen
A1  - Salo, Heikki
A1  - Seiler, Michael
A1  - Hoffmann, Holger
A1  - Spahn, Frank
T1  - Hydrodynamic Simulations of Moonlet-induced Propellers in Saturn's Rings
BT  - Application to Bleriot
JF  - The astronomical journal
N2  - One of the biggest successes of the Cassini mission is the detection of small moons (moonlets) embedded in Saturns rings that cause S-shaped density structures in their close vicinity, called propellers. Here, we present isothermal hydrodynamic simulations of moonlet-induced propellers in Saturn's A ring that denote a further development of the original model. We find excellent agreement between these new hydrodynamic and corresponding N-body simulations. Furthermore, the hydrodynamic simulations confirm the predicted scaling laws and the analytical solution for the density in the propeller gaps. Finally, this mean field approach allows us to simulate the pattern of the giant propeller Blériot, which is too large to be modeled by direct N-body simulations. Our results are compared to two stellar occultation observations by the Cassini Ultraviolet Imaging Spectrometer (UVIS), which intersect the propeller Blériot. Best fits to the UVIS optical depth profiles are achieved for a Hill radius of 590 m, which implies a moonlet diameter of about 860 m. Furthermore, the model favors a kinematic shear viscosity of the surrounding ring material of ν0 = 340 cm2 s−1, a dispersion velocity in the range of 0.3 cm s−1 < c0 < 1.5 cm s−1, and a fairly high bulk viscosity 7 < ξ0/ν0 < 17. These large transport values might be overestimated by our isothermal ring model and should be reviewed by an extended model including thermal fluctuations.
KW  - diffusion
KW  - hydrodynamics
KW  - planets and satellites: rings
Y1  - 2018
U6  - https://doi.org/10.3847/1538-3881/aaed44
SN  - 0004-6256
SN  - 1538-3881
VL  - 157
IS  - 1
PB  - IOP Publishing Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Liemohn, Michael W.
A1  - McCollough, James P.
A1  - Jordanova, Vania K.
A1  - Ngwira, Chigomezyo M.
A1  - Morley, Steven K.
A1  - Cid, Consuelo
A1  - Tobiska, W. Kent
A1  - Wintoft, Peter
A1  - Ganushkina, Natalia Yu
A1  - Welling, Daniel T.
A1  - Bingham, Suzy
A1  - Balikhin, Michael A.
A1  - Opgenoorth, Hermann J.
A1  - Engel, Miles A.
A1  - Weigel, Robert S.
A1  - Singer, Howard J.
A1  - Buresova, Dalia
A1  - Bruinsma, Sean
A1  - Zhelavskaya, Irina S.
A1  - Shprits, Yuri Y.
A1  - Vasile, Ruggero
T1  - Model Evaluation Guidelines for Geomagnetic Index Predictions
JF  - Space Weather: The International Journal of Research and Applications
N2  - Geomagnetic indices are convenient quantities that distill the complicated physics of some region or aspect of near-Earth space into a single parameter. Most of the best-known indices are calculated from ground-based magnetometer data sets, such as Dst, SYM-H, Kp, AE, AL, and PC. Many models have been created that predict the values of these indices, often using solar wind measurements upstream from Earth as the input variables to the calculation. This document reviews the current state of models that predict geomagnetic indices and the methods used to assess their ability to reproduce the target index time series. These existing methods are synthesized into a baseline collection of metrics for benchmarking a new or updated geomagnetic index prediction model. These methods fall into two categories: (1) fit performance metrics such as root-mean-square error and mean absolute error that are applied to a time series comparison of model output and observations and (2) event detection performance metrics such as Heidke Skill Score and probability of detection that are derived from a contingency table that compares model and observation values exceeding (or not) a threshold value. A few examples of codes being used with this set of metrics are presented, and other aspects of metrics assessment best practices, limitations, and uncertainties are discussed, including several caveats to consider when using geomagnetic indices. Plain Language Summary One aspect of space weather is a magnetic signature across the surface of the Earth. The creation of this signal involves nonlinear interactions of electromagnetic forces on charged particles and can therefore be difficult to predict. The perturbations that space storms and other activity causes in some observation sets, however, are fairly regular in their pattern. Some of these measurements have been compiled together into a single value, a geomagnetic index. Several such indices exist, providing a global estimate of the activity in different parts of geospace. Models have been developed to predict the time series of these indices, and various statistical methods are used to assess their performance at reproducing the original index. Existing studies of geomagnetic indices, however, use different approaches to quantify the performance of the model. This document defines a standardized set of statistical analyses as a baseline set of comparison tools that are recommended to assess geomagnetic index prediction models. It also discusses best practices, limitations, uncertainties, and caveats to consider when conducting a model assessment.
Y1  - 2018
U6  - https://doi.org/10.1029/2018SW002067
SN  - 1542-7390
VL  - 16
IS  - 12
SP  - 2079
EP  - 2102
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Saikin, Anthony A.
A1  - Jordanova, Vania K.
A1  - Zhang, J. C.
A1  - Smith, C. W.
A1  - Spence, H. E.
A1  - Larsen, B. A.
A1  - Reeves, G. D.
A1  - Torbert, R. B.
A1  - Kletzing, C. A.
A1  - Zhelayskaya, I. S.
A1  - Shprits, Yuri Y.
T1  - Comparing simulated and observed EMIC wave amplitudes using in situ Van
JF  - Journal of Atmospheric and Solar-Terrestrial Physics
N2  - We perform a statistical study calculating electromagnetic ion cyclotron (EMIC) wave amplitudes based off in situ plasma measurements taken by the Van Allen Probes’ (1.1–5.8 Re) Helium, Oxygen, Proton, Electron (HOPE) instrument. Calculated wave amplitudes are compared to EMIC waves observed by the Electric and Magnetic Field Instrument Suite and Integrated Science on board the Van Allen Probes during the same period. The survey covers a 22-month period (1 November 2012 to 31 August 2014), a full Van Allen Probe magnetic local time (MLT) precession. The linear theory proxy was used to identify EMIC wave events with plasma conditions favorable for EMIC wave excitation. Two hundred and thirty-two EMIC wave events (103 H+-band and 129 He+-band) were selected for this comparison. Nearly all events selected are observed beyond L = 4. Results show that calculated wave amplitudes exclusively using the in situ HOPE measurements produce amplitudes too low compared to the observed EMIC wave amplitudes. Hot proton anisotropy (Ahp) distributions are asymmetric in MLT within the inner (L < 7) magnetosphere with peak (minimum) Ahp, ∼0.81 to 1.00 (∼0.62), observed in the dawn (dusk), 0000 < MLT ≤ 1200 (1200 < MLT ≤ 2400), sectors. Measurements of Ahp are found to decrease in the presence of EMIC wave activity. Ahp amplification factors are determined and vary with respect to EMIC wave-band and MLT. He+-band events generally require double (quadruple) the measured Ahp for the dawn (dusk) sector to reproduce the observed EMIC wave amplitudes.
KW  - EMIC waves
KW  - Van Allen Probes
KW  - Linear theory
KW  - Wave generation
Y1  - 2018
U6  - https://doi.org/10.1016/j.jastp.2018.01.024
SN  - 1364-6826
SN  - 1879-1824
VL  - 177
SP  - 190
EP  - 201
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Schmälzlin, Elmar Gerd
A1  - Moralejo, Benito
A1  - Gersonde, Ingo
A1  - Schleusener, Johannes
A1  - Darvin, Maxim E.
A1  - Thiede, Gisela
A1  - Roth, Martin M.
T1  - Nonscanning large-area Raman imaging for ex vivo/in vivo skin cancer discrimination
JF  - Journal of biomedical optics
N2  - Imaging Raman spectroscopy can be used to identify cancerous tissue. Traditionally, a step-by-step scanning of the sample is applied to generate a Raman image, which, however, is too slow for routine examination of patients. By transferring the technique of integral field spectroscopy (IFS) from astronomy to Raman imaging, it becomes possible to record entire Raman images quickly within a single exposure, without the need for a tedious scanning procedure. An IFS-based Raman imaging setup is presented, which is capable of measuring skin ex vivo or in vivo. It is demonstrated how Raman images of healthy and cancerous skin biopsies were recorded and analyzed. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.
KW  - Raman spectroscopy
KW  - cancer diagnosis
KW  - Raman imaging
KW  - multichannel
KW  - astronomy
KW  - epidermis
KW  - dermis
Y1  - 2018
U6  - https://doi.org/10.1117/1.JBO.23.10.105001
SN  - 1083-3668
SN  - 1560-2281
VL  - 23
IS  - 10
PB  - SPIE
CY  - Bellingham
ER  - 
TY  - JOUR
A1  - Mann, Michael E.
A1  - Rahmstorf, Stefan
A1  - Kornhuber, Kai
A1  - Steinman, Byron A.
A1  - Miller, Sonya K.
A1  - Petri, Stefan
A1  - Coumou, Dim
T1  - Projected changes in persistent extreme summer weather events
BT  - The role of quasi-resonant amplification
JF  - Science Advances
N2  - Persistent episodes of extreme weather in the Northern Hemisphere summer have been associated with high-amplitude quasi-stationary atmospheric Rossby waves, with zonal wave numbers 6 to 8 resulting from the phenomenon of quasi-resonant amplification (QRA). A fingerprint for the occurrence of QRA can be defined in terms of the zonally averaged surface temperature field. Examining state-of-the-art [Coupled Model Intercomparison Project Phase 5 (CMIP5)] climate model projections, we find that QRA events are likely to increase by similar to 50% this century under business-as-usual carbon emissions, but there is considerable variation among climate models. Some predict a near tripling of QRA events by the end of the century, while others predict a potential decrease. Models with amplified Arctic warming yield the most pronounced increase in QRA events. The projections are strongly dependent on assumptions regarding the nature of changes in radiative forcing associated with anthropogenic aerosols over the next century. One implication of our findings is that a reduction in midlatitude aerosol loading could actually lead to Arctic de-amplification this century, ameliorating potential increases in persistent extreme weather events.
Y1  - 2018
U6  - https://doi.org/10.1126/sciadv.aat3272
SN  - 2375-2548
VL  - 4
IS  - 10
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Richter, Philipp
A1  - Fox, Andrew J.
A1  - Wakker, Bart P.
A1  - Howk, J. Christopher
A1  - Lehner, Nicolas
A1  - Barger, Kathleen A.
A1  - Lockman, Felix J.
T1  - New constraints on the nature and origin of the leading arm of the magellanic stream
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present a new precision measurement of gas-phase abundances of S, O, N, Si, Fe, P, Al, Ca as well as molecular hydrogen (H-2) in the Leading Arm (region II, LA II) of the Magellanic Stream (MS) toward the Seyfert galaxy NGC 3783. The results are based on high-quality archival ultraviolet/optical/radio data from various different instruments (HST/STIS, FUSE, AAT, GBT, GB140 ft, ATCA). Our study updates previous results from lower-resolution data and provides for the first time a self-consistent component model of the complex multiphase absorber, delivering important constraints on the nature and origin of LA II. We derive a uniform, moderate a abundance in the two main absorber groups at +245 and +190 km s(-1) of alpha/H = 0.30 +/- 0.05 solar, a low nitrogen abundance of N/H = 0.05 +/- 0.01 solar, and a high dust content with substantial dust depletion values for Si, Fe, Al, and Ca. These a, N, and dust abundances in LA II are similar to those observed in the Small Magellanic Cloud (SMC). From the analysis of the H2 absorption, we determine a high thermal pressure of P/k approximate to 1680 K cm(-3) in LA II, in line with the idea that LA II is located in the inner Milky Way halo at a z-height of < 20 kpc, where it hydrodynamically interacts with the ambient hot coronal gas. Our study supports a scenario in which LA II stems from the breakup of a metal- and dust-enriched progenitor cloud that was recently (200-500 Myr ago) stripped from the SMC.
KW  - Galaxy: evolution
KW  - Galaxy: halo
KW  - ISM: abundances
KW  - Magellanic Clouds
KW  - quasars: absorption lines
Y1  - 2018
U6  - https://doi.org/10.3847/1538-4357/aadd0f
SN  - 0004-637X
SN  - 1538-4357
VL  - 865
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - von Reppert, Alexander
A1  - Willig, Lisa
A1  - Pudell, Jan-Etienne
A1  - Roessle, M.
A1  - Leitenberger, Wolfram
A1  - Herzog, Marc
A1  - Ganss, F.
A1  - Hellwig, O.
A1  - Bargheer, Matias
T1  - Ultrafast laser generated strain in granular and continuous FePt thin films
JF  - Applied physics letters
N2  - We employ ultrafast X-ray diffraction to compare the lattice dynamics of laser-excited continuous and granular FePt films on MgO (100) substrates. Contrary to recent results on free-standing granular films, we observe in both cases a pronounced and long-lasting out-of-plane expansion. We attribute this discrepancy to the in-plane expansion, which is suppressed by symmetry in continuous films. Granular films on substrates are less constrained and already show a reduced out-of-plane contraction. Via the Poisson effect, out-of-plane contractions drive in-plane expansion and vice versa. Consistently, the granular film exhibits a short-lived out-of-plane contraction driven by ultrafast demagnetization which is followed by a reduced and delayed expansion. From the acoustic reflections of the observed strain waves at the film-substrate interface, we extract a 13% reduction of the elastic constants in thin 10 nm FePt films compared to bulk-like samples. (C) 2018 Author(s).
Y1  - 2018
U6  - https://doi.org/10.1063/1.5050234
SN  - 0003-6951
SN  - 1077-3118
VL  - 113
IS  - 12
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Archer, A.
A1  - Benbow, W.
A1  - Bird, R.
A1  - Brose, Robert
A1  - Buchovecky, M.
A1  - Buckley, J. H.
A1  - Bugaev, V.
A1  - Connolly, M. P.
A1  - Cui, W.
A1  - Daniel, M. K.
A1  - Feng, Q.
A1  - Finley, J. P.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Gillanders, G.
A1  - Huetten, M.
A1  - Hanna, D.
A1  - Hervet, O.
A1  - Holder, J.
A1  - Hughes, G.
A1  - Humensky, T. B.
A1  - Johnson, C. A.
A1  - Kaaret, P.
A1  - Kar, P.
A1  - Kelley-Hoskins, N.
A1  - Kertzman, M.
A1  - Kieda, D.
A1  - Krause, M.
A1  - Krennrich, F.
A1  - Kumar, S.
A1  - Lang, M. J.
A1  - Lin, T. T. Y.
A1  - Maier, G.
A1  - McArthur, S.
A1  - Moriarty, P.
A1  - Mukherjee, R.
A1  - Ong, R. A.
A1  - Otte, A. N.
A1  - Petrashyk, A.
A1  - Pohl, M.
A1  - Pueschel, Elisa
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reynolds, P. T.
A1  - Richards, G. T.
A1  - Roache, E.
A1  - Rulten, C.
A1  - Sadeh, I.
A1  - Santander, M.
A1  - Sembroski, G. H.
A1  - Staszak, D.
A1  - Sushch, I.
A1  - Wakely, S. P.
A1  - Wells, R. M.
A1  - Wilcox, P.
A1  - Wilhelm, Alina
A1  - Williams, D. A.
A1  - Williamson, T. J.
A1  - Zitzer, B.
T1  - Measurement of cosmic-ray electrons at TeV energies by VERITAS
JF  - Physical review : D, Particles, fields, gravitation, and cosmology
N2  - Cosmic-ray electrons and positrons (CREs) at GeV-TeV energies are a unique probe of our local Galactic neighborhood. CREs lose energy rapidly via synchrotron radiation and inverse-Compton scattering processes while propagating within the Galaxy, and these losses limit their propagation distance. For electrons with TeV energies, the limit is on the order of a kiloparsec. Within that distance, there are only a few known astrophysical objects capable of accelerating electrons to such high energies. It is also possible that the CREs are the products of the annihilation or decay of heavy dark matter (DM) particles. VERITAS, an array of imaging air Cherenkov telescopes in southern Arizona, is primarily utilized for gamma-ray astronomy but also simultaneously collects CREs during all observations. We describe our methods of identifying CREs in VERITAS data and present an energy spectrum, extending from 300 GeV to 5 TeV, obtained from approximately 300 hours of observations. A single power-law fit is ruled out in VERITAS data. We find that the spectrum of CREs is consistent with a broken power law, with a break energy at 710 +/- 40(stat) +/- 140(syst) GeV.
Y1  - 2018
U6  - https://doi.org/10.1103/PhysRevD.98.062004
SN  - 2470-0010
SN  - 2470-0029
VL  - 98
IS  - 6
PB  - American Physical Society
CY  - College Park
ER  -