TY  - JOUR
A1  - Ni, Lei
A1  - Kliem, Bernhard
A1  - Lin, Jun
A1  - Wu, Ning
T1  - Fast magnetic reconnection in the solar chromosphere mediated by theplasmoid instability
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - Magnetic reconnection in the partially ionized solar chromosphere is studied in 2.5 dimensional magnetohydrodynamic simulations including radiative cooling and ambipolar diffusion. A Harris current sheet with and without a guide field is considered. Characteristic values of the parameters in the middle chromosphere imply a high magnetic Reynolds number of similar to 10(6)-10(7) in the present simulations. Fast magnetic reconnection then develops as a consequence of the plasmoid instability without the need to invoke anomalous resistivity enhancements. Multiple levels of the instability are followed as it cascades to smaller scales, which approach the ion inertial length. The reconnection rate, normalized to the asymptotic values of magnetic field and Alfven velocity in the inflow region, reaches values in the range similar to 0.01-0.03 throughout the cascading plasmoid formation and for zero as well as for strong guide field. The outflow velocity reaches approximate to 40 km s(-1). Slow-mode shocks extend from the X-points, heating the plasmoids up to similar to 8 x 10(4) K. In the case of zero guide field, the inclusion of both ambipolar diffusion and radiative cooling causes a rapid thinning of the current sheet (down to similar to 30 m) and early formation of secondary islands. Both of these processes have very little effect on the plasmoid instability for a strong guide field. The reconnection rates, temperature enhancements, and upward outflow velocities from the vertical current sheet correspond well to their characteristic values in chromospheric jets.
KW  - magnetic reconnection
KW  - magnetohydrodynamics (MHD)
KW  - radiation: dynamics
KW  - Sun: activity
KW  - Sun: chromosphere
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/799/1/79
SN  - 0004-637X
SN  - 1538-4357
VL  - 799
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Nichols, Joy
A1  - Huenemoerder, David P.
A1  - Corcoran, Michael F.
A1  - Waldron, Wayne
A1  - Naze, Yael
A1  - Pollock, Andy M. T.
A1  - Moffat, Anthony F. J.
A1  - Lauer, Jennifer
A1  - Shenar, Tomer
A1  - Russell, Christopher M. P.
A1  - Richardson, Noel D.
A1  - Pablo, Herbert
A1  - Evans, Nancy Remage
A1  - Hamaguchi, Kenji
A1  - Gull, Theodore
A1  - Hamann, Wolf-Rainer
A1  - Oskinova, Lida
A1  - Ignace, Rosina
A1  - Hoffman, Jennifer L.
A1  - Hole, Karen Tabetha
A1  - Lomax, Jamie R.
T1  - A COORDINATED X-RAY AND OPTICAL CAMPAIGN OF THE NEAREST MASSIVE ECLIPSING BINARY, delta ORIONIS Aa. II. X-RAY VARIABILITY
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the delta Ori Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of approximate to 479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range of 5-25 is is confirmed, with a maximum amplitude of about +/- 15% within a single approximate to 125 ks observation. Periods of 4.76 and 2.04 days are found in the total X-ray flux, as well as an apparent overall increase in the flux level throughout the nine-day observational campaign. Using 40 ks contiguous spectra derived from the original observations, we investigate the variability of emission line parameters and ratios. Several emission lines are shown to be variable, including S XV, Si XIII, and Ne IX. For the first time, variations of the X-ray emission line widths as a function of the binary phase are found in a binary system, with the smallest widths at phi = 0.0 when the secondary delta Ori Aa2 is at the inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds, we relate the emission line width variability to the presence of a wind cavity created by a wind-wind collision, which is effectively void of embedded wind shocks and is carved out of the X-ray-producing primary wind, thus producing phase-locked X-ray variability.
KW  - binaries: close
KW  - binaries: eclipsing
KW  - stars: individual ([HD 36486]delta Ori A)
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/809/2/133
SN  - 0004-637X
SN  - 1538-4357
VL  - 809
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Niebuhr, Mario
A1  - Zink, Christof
A1  - Jechow, Andreas
A1  - Heuer, Axel
A1  - Glebov, Leonid B.
A1  - Menzel, Ralf
T1  - Mode stabilization of a laterally structured broad area diode laser using an external volume Bragg grating
JF  - Optics express : the international electronic journal of optics
N2  - An external volume Bragg grating (VBG) is used for transverse and longitudinal mode stabilization of a broad area diode laser (BAL) with an on-chip transverse Bragg resonance (TBR) grating. The internal TBR grating defines a transverse low-loss mode at a specific propagation angle inside the BAL. Selection of the TBR mode was realized via the angular geometry of an external resonator assembly consisting of the TBR BAL and a feedback element. A feedback mirror provides near diffraction limited and spectral narrow output in the TBR mode albeit requiring an intricate alignment procedure. If feedback is provided via a VBG, adjustment proves to be far less critical and higher output powers were achieved. Moreover, additional modulation in the far field distribution became discernible allowing for a better study of the TBR concept. (C) 2015 Optical Society of America
Y1  - 2015
U6  - https://doi.org/10.1364/OE.23.012394
SN  - 1094-4087
VL  - 23
IS  - 9
SP  - 12394
EP  - 12400
PB  - Optical Society of America
CY  - Washington
ER  - 
TY  - JOUR
A1  - Niedl, Robert Raimund
A1  - Beta, Carsten
T1  - Hydrogel-driven paper-based microfluidics
JF  - LAB on a chip : miniaturisation for chemistry and biology
N2  - Paper-based microfluidics provide an inexpensive, easy to use technology for point-of-care diagnostics in developing countries. Here, we combine paper-based microfluidic devices with responsive hydrogels to add an entire new class of functions to these versatile low-cost fluidic systems. The hydrogels serve as fluid reservoirs. In response to an external stimulus, e.g. an increase in temperature, the hydrogels collapse and release fluid into the structured paper substrate. In this way, chemicals that are either stored on the paper substrate or inside the hydrogel pads can be dissolved, premixed, and brought to reaction to fulfill specific analytic tasks. We demonstrate that multi-step sequences of chemical reactions can be implemented in a paper-based system and operated without the need for external precision pumps. We exemplify this technology by integrating an antibody-based E. coli test on a small and easy to use paper device.
Y1  - 2015
U6  - https://doi.org/10.1039/c5lc00276a
SN  - 1473-0197
SN  - 1473-0189
VL  - 15
IS  - 11
SP  - 2452
EP  - 2459
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Oberg, H.
A1  - Gladh, Jörgen
A1  - Anniyev, Toyli
A1  - Beye, Martin
A1  - Coffee, Ryan
A1  - Föhlisch, Alexander
A1  - Katayama, T.
A1  - Kaya, Sarp
A1  - LaRue, Jerry
A1  - Mogelhoj, Andreas
A1  - Nordlund, Dennis
A1  - Ogasawara, Hirohito
A1  - Schlotter, William F.
A1  - Sellberg, Jonas A.
A1  - Sorgenfrei, Nomi
A1  - Turner, Joshua J.
A1  - Wolf, Martin
A1  - Wurth, W.
A1  - Ostrom, Henrik
A1  - Nilsson, Anders
A1  - Norskov, Jens K.
A1  - Pettersson, Lars G. M.
T1  - Optical laser-induced CO desorption from Ru(0001) monitored with a free-electron X-ray laser: DFT prediction and X-ray confirmation of a precursor state
JF  - Surface science
N2  - We present density functional theory modeling of time-resolved optical pump/X-ray spectroscopic probe data of CO desorption from Ru(0001). The BEEF van der Waals functional predicts a weakly bound state as a precursor to desorption. The optical pump leads to a near-instantaneous (<100 fs) increase of the electronic temperature to nearly 7000 K. The temperature evolution and energy transfer between electrons, substrate phonons and adsorbate is described by the two-temperature model and found to equilibrate on a timescale of a few picoseconds to an elevated local temperature of similar to 2000K. Estimating the free energy based on the computed potential of mean force along the desorption path, we find an entropic barrier to desorption (and by time-reversal also to adsorption). This entropic barrier separates the chemisorbed and precursor states, and becomes significant at the elevated temperature of the experiment (similar to 1.4 eV at 2000 K). Experimental pump-probe X-ray absorption/X-ray emission spectroscopy indicates population of a precursor state to desorption upon laser-excitation of the system (Dell'Angela et al., 2013). Computing spectra along the desorption path confirms the picture of a weakly bound transient state arising from ultrafast heating of the metal substrate. (C) 2015 Elsevier B.V. All rights reserved.
KW  - CO desorption
KW  - Potential of mean force
KW  - Two-temperature model
KW  - Pump-probe
KW  - X-ray spectroscopy
KW  - Density functional theory
Y1  - 2015
U6  - https://doi.org/10.1016/j.susc.2015.03.011
SN  - 0039-6028
SN  - 1879-2758
VL  - 640
SP  - 80
EP  - 88
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Orienti, M.
A1  - Finke, J.
A1  - Raiteri, C. M.
A1  - Hovatta, T.
A1  - Larsson, J.
A1  - Max-Moerbeck, W.
A1  - Perkins, J.
A1  - Readhead, A. C. S.
A1  - Richards, J. L.
A1  - Beilicke, M.
A1  - Benbow, W.
A1  - Berger, K.
A1  - Bird, R.
A1  - Bugaev, V.
A1  - Cardenzana, J. V.
A1  - Cerruti, M.
A1  - Chen, Xuhui
A1  - Ciupik, L.
A1  - Dickinson, H. J.
A1  - Eisch, J. D.
A1  - Errando, M.
A1  - Falcone, A.
A1  - Finley, J. P.
A1  - Fleischhack, H.
A1  - Fortin, P.
A1  - Fortson, L.
A1  - Furniss, A.
A1  - Gerard, L.
A1  - Gillanders, G. H.
A1  - Griffiths, S. T.
A1  - Grube, J.
A1  - Gyuk, G.
A1  - Hakansson, Nils
A1  - Holder, J.
A1  - Humensky, T. B.
A1  - Kar, P.
A1  - Kertzman, M.
A1  - Khassen, Y.
A1  - Kieda, D.
A1  - Krennrich, F.
A1  - Kumar, S.
A1  - Lang, M. J.
A1  - Maier, G.
A1  - McCann, A.
A1  - Meagher, K.
A1  - Moriarty, P.
A1  - Mukherjee, R.
A1  - Nieto, D.
A1  - Ong, R. A.
A1  - Otte, A. N.
A1  - Pohl, Manuela
A1  - Popkow, A.
A1  - Prokoph, H.
A1  - Pueschel, Elisa
A1  - Quinn, J.
A1  - Ragan, K.
A1  - Reynolds, P. T.
A1  - Richards, G. T.
A1  - Roache, E.
A1  - Rousselle, J.
A1  - Santander, M.
A1  - Sembroski, G. H.
A1  - Smith, A. W.
A1  - Staszak, D.
A1  - Telezhinsky, Igor O.
A1  - Tucci, J. V.
A1  - Tyler, J.
A1  - Varlotta, A.
A1  - Vassiliev, V. V.
A1  - Wakely, S. P.
A1  - Weinstein, A.
A1  - Welsing, R.
A1  - Williams, D. A.
A1  - Zitzer, B.
T1  - The most powerful flaring activity from the NLSyl PMN J0948+0022
JF  - Monthly notices of the Royal Astronomical Society
N2  - We report on multifrequency observations performed during 2012 December-2013 August of the first narrow-line Seyfert 1 galaxy detected in gamma-rays, PMN J0948+0022 (z = 0.5846). A y -ray flare was observed by the Large Area Telescope on board Fermi during 2012 December-2013 January, reaching a daily peak flux in the 0.1-100 GeV energy range of (155 31) x 10 8 ph cm(-2) S-1 on 2013 January 1, corresponding to an apparent isotropic luminosity of similar to 1.5 x 1048 erg s(-1). The y -ray flaring period triggered Swift and Very Energetic Radiation Imaging Telescope Array System (VERITAS) observations in addition to radio and optical monitoring by Owens Valley Radio Observatory, Monitoring Of Jets in Active galactic nuclei with VLBA Experiments, and Catalina Real-time Transient Survey. A strong flare was observed in optical, UV, and X-rays on 2012 December 30, quasi-simultaneously to the y -ray flare, reaching a record flux for this source from optical to y gamma-rays. VERITAS observations at very high energy (E > 100 GeV) during 2013 January 6-17 resulted in an upper limit of F>0.2 Trev < 4.0 x 10(-12) ph cm(-2) s(-1). We compared the spectral energy distribution (SED) of the flaring state in 2013 January with that of an intermediate state observed in 2011. The two SEDs, modelled as synchrotron emission and an external Compton scattering of seed photons from a dust torus, can be modelled by changing both the electron distribution parameters and the magnetic field.
KW  - galaxies: active-galaxies: individual: PMN J0948+0022
KW  - galaxies: nuclei
KW  - galaxies: Seyfert
KW  - gamma-rays: general
Y1  - 2015
U6  - https://doi.org/10.1093/mnras/stu2251
SN  - 0035-8711
SN  - 1365-2966
VL  - 446
IS  - 3
SP  - 2456
EP  - 2467
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Oskinova, Lida
T1  - X-ray emission from single WR stars
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - In this review I briefly summarize our knowledge of the X-ray emission from single WN, WC, and WO stars. These stars have relatively modest X-ray luminosities, typically not exceeding 1L⊙. The analysis of X-ray spectra usually reveals thermal plasma with temperatures reaching a few x10 MK. X-ray variability is detected in some WN stars. At present we don't fully understand how X-ray radiation in produced in WR stars, albeit there are some promising research avenues, such as the presence of CIRs in the winds of some stars. To fully understand WR stars we need to unravel mechanisms of X-ray production in their winds.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88228
SP  - 295
EP  - 300
ER  - 
TY  - JOUR
A1  - Oskinova, Lida
A1  - Todt, Helge Tobias
A1  - Huenemoerder, David P.
A1  - Hubrig, Swetlana
A1  - Ignace, Richard
A1  - Hamann, Wolf-Rainer
A1  - Balona, Luis
T1  - On X-ray pulsations in beta Cephei-type variables
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. beta Cep-type variables are early B-type stars that are characterized by oscillations observable in their optical light curves. At least one beta Cep-variable also shows periodic variability in X-rays.
 Aims. Here we study the X-ray light curves in a sample of beta Cep-variables to investigate how common X-ray pulsations are for this type of stars.
 Methods. We searched the Chandra and XMM-Newton X-ray archives and selected stars that were observed by these telescopes for at least three optical pulsational periods. We retrieved and analyzed the X-ray data for kappa Sco, beta Cru, and alpha Vir. The X-ray light curves of these objects were studied to test for their variability and periodicity.
 Results. While there is a weak indication for X-ray variability in beta Cru, we find no statistically significant evidence of X-ray pulsations in any of our sample stars. This might be due either to the insufficient data quality or to the physical lack of modulations. New, more sensitive observations should settle this question.
KW  - stars: massive
KW  - stars: variables: general
KW  - X-rays: stars
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201525908
SN  - 0004-6361
SN  - 1432-0746
VL  - 577
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Ostrom, H.
A1  - Oberg, H.
A1  - Xin, H.
A1  - Larue, J.
A1  - Beye, Martin
A1  - Gladh, J.
A1  - Ng, M. L.
A1  - Sellberg, J. A.
A1  - Kaya, S.
A1  - Mercurio, G.
A1  - Nordlund, D.
A1  - Hantschmann, Markus
A1  - Hieke, F.
A1  - Kuehn, D.
A1  - Schlotter, W. F.
A1  - Dakovski, G. L.
A1  - Turner, J. J.
A1  - Minitti, M. P.
A1  - Mitra, A.
A1  - Moeller, S. P.
A1  - Föhlisch, Alexander
A1  - Wolf, M.
A1  - Wurth, W.
A1  - Persson, Mats
A1  - Norskov, J. K.
A1  - Abild-Pedersen, Frank
A1  - Ogasawara, Hirohito
A1  - Pettersson, Lars G. M.
A1  - Nilsson, A.
T1  - Probing the transition state region in catalytic CO oxidation on Ru
JF  - Science
N2  - Femtosecond x-ray laser pulses are used to probe the carbon monoxide (CO) oxidation reaction on ruthenium (Ru) initiated by an optical laser pulse. On a time scale of a few hundred femtoseconds, the optical laser pulse excites motions of CO and oxygen (O) on the surface, allowing the reactants to collide, and, with a transient close to a picosecond (ps), new electronic states appear in the OK-edge x-ray absorption spectrum. Density functional theory calculations indicate that these result from changes in the adsorption site and bond formation between CO and O with a distribution of OC-O bond lengths close to the transition state (TS). After 1 ps, 10% of the CO populate the TS region, which is consistent with predictions based on a quantum oscillator model.
Y1  - 2015
U6  - https://doi.org/10.1126/science.1261747
SN  - 0036-8075
SN  - 1095-9203
VL  - 347
IS  - 6225
SP  - 978
EP  - 982
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Pablo, Herbert
A1  - Richardson, Noel D.
A1  - Moffat, Anthony F. J.
A1  - Corcoran, Michael
A1  - Shenar, Tomer
A1  - Benvenuto, Omar
A1  - Fuller, Jim
A1  - Naze, Yael
A1  - Hoffman, Jennifer L.
A1  - Miroshnichenko, Anatoly
A1  - Apellaniz, Jesus Maiz
A1  - Evans, Nancy
A1  - Eversberg, Thomas
A1  - Gayley, Ken
A1  - Gull, Ted
A1  - Hamaguchi, Kenji
A1  - Hamann, Wolf-Rainer
A1  - Henrichs, Huib
A1  - Hole, Tabetha
A1  - Ignace, Richard
A1  - Iping, Rosina
A1  - Lauer, Jennifer
A1  - Leutenegger, Maurice
A1  - Lomax, Jamie
A1  - Nichols, Joy
A1  - Oskinova, Lida
A1  - Owocki, Stan
A1  - Pollock, Andy
A1  - Russell, Christopher M. P.
A1  - Waldron, Wayne
A1  - Buil, Christian
A1  - Garrel, Thierry
A1  - Graham, Keith
A1  - Heathcote, Bernard
A1  - Lemoult, Thierry
A1  - Li, Dong
A1  - Mauclaire, Benjamin
A1  - Potter, Mike
A1  - Ribeiro, Jose
A1  - Matthews, Jaymie
A1  - Cameron, Chris
A1  - Guenther, David
A1  - Kuschnig, Rainer
A1  - Rowe, Jason
A1  - Rucinski, Slavek
A1  - Sasselov, Dimitar
A1  - Weiss, Werner
T1  - A coordinated X-Ray and optical campaign of the nearest massive eclipsing binary, delta ORIONIS Aa. III. Analysis of optical photometric (most) and spectroscopic (ground based) variations
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We report on both high-precision photometry from the Microvariability and Oscillations of Stars (MOST) space telescope and ground-based spectroscopy of the triple system delta Ori A, consisting of a binary O9.5II+early-B (Aa1 and Aa2) with P = 5.7 days, and a more distant tertiary (O9 IV P > 400 years). This data was collected in concert with X-ray spectroscopy from the Chandra X-ray Observatory. Thanks to continuous coverage for three weeks, the MOST light curve reveals clear eclipses between Aa1 and Aa2 for the first time in non-phased data. From the spectroscopy, we have a well-constrained radial velocity (RV) curve of Aa1. While we are unable to recover RV variations of the secondary star, we are able to constrain several fundamental parameters of this system and determine an approximate mass of the primary using apsidal motion. We also detected second order modulations at 12 separate frequencies with spacings indicative of tidally influenced oscillations. These spacings have never been seen in a massive binary, making this system one of only a handful of such binaries that show evidence for tidally induced pulsations.
KW  - binaries: close
KW  - binaries: eclipsing
KW  - stars: early-type
KW  - stars: individual (delta Ori A)
KW  - stars: mass-loss
KW  - stars: variables: general
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/809/2/134
SN  - 0004-637X
SN  - 1538-4357
VL  - 809
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Parezanovic, Vladimir
A1  - Laurentie, Jean-Charles
A1  - Fourment, Carine
A1  - Delville, Joel
A1  - Bonnet, Jean-Paul
A1  - Spohn, Andreas
A1  - Duriez, Thomas
A1  - Cordier, Laurent
A1  - Noack, Bernd R.
A1  - Abel, Markus
A1  - Segond, Marc
A1  - Shaqarin, Tamir
A1  - Brunton, Steven L.
T1  - Mixing layer manipulation experiment from open-loop forcing to closed-loop machine learning control
JF  - Flow, turbulence and combustion : an international journal published in association with ERCOFTAC
KW  - Shear flow
KW  - Turbulence
KW  - Active flow control
KW  - Extremum seeking
KW  - POD
KW  - Machine learning
KW  - Genetic programming
Y1  - 2015
U6  - https://doi.org/10.1007/s10494-014-9581-1
SN  - 1386-6184
SN  - 1573-1987
VL  - 94
IS  - 1
SP  - 155
EP  - 173
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Pavlyukevich, Ilya
A1  - Li, Yongge
A1  - Xu, Yong
A1  - Chechkin, Aleksei V.
T1  - Directed transport induced by spatially modulated Levy flights
JF  - Journal of physics : A, Mathematical and theoretical
N2  - In this paper we study the dynamics of a particle in a ratchet potential subject to multiplicative alpha-stable Levy noise, alpha is an element of(0, 2), in the limit of a noise amplitude epsilon -> 0. We compare the dynamics for Ito and Marcus multiplicative noises and obtain the explicit asymptotics of the escape time in the wells and transition probabilities between the wells. A detailed analysis of the noise-induced current is performed for the Seebeck ratchet with a weak multiplicative noise for alpha is an element of(0, 2].
KW  - Levy flights
KW  - multiplicative noise
KW  - Seebeck ratchet
KW  - directed transport
Y1  - 2015
U6  - https://doi.org/10.1088/1751-8113/48/49/495004
SN  - 1751-8113
SN  - 1751-8121
VL  - 48
IS  - 49
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Perez-Velazquez, Jose Luis
A1  - Erra, Ramon Guevara
A1  - Rosenblum, Michael
T1  - The Epileptic Thalamocortical Network is a Macroscopic Self-Sustained Oscillator: Evidence from Frequency-Locking Experiments in Rat Brains
JF  - Scientific reports
N2  - The rhythmic activity observed in nervous systems, in particular in epilepsies and Parkinson's disease, has often been hypothesized to originate from a macroscopic self-sustained neural oscillator. However, this assumption has not been tested experimentally. Here we support this viewpoint with in vivo experiments in a rodent model of absence seizures, by demonstrating frequency locking to external periodic stimuli and finding the characteristic Arnold tongue. This result has important consequences for developing methods for the control of brain activity, such as seizure cancellation.
Y1  - 2015
U6  - https://doi.org/10.1038/srep08423
SN  - 2045-2322
VL  - 5
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Piatti, Andres E.
A1  - de Grijs, Richard
A1  - Ripepi, Vincenzo
A1  - Ivanov, Valentin D.
A1  - Cioni, Maria-Rosa L.
A1  - Marconi, Marcella
A1  - Rubele, Stefano
A1  - Bekki, Kenji
A1  - For, Bi-Qing
T1  - The VMC survey - XVI. Spatial variation of the cluster formation activity in the innermost regions of the Large Magellanic Cloud
JF  - Monthly notices of the Royal Astronomical Society
KW  - techniques: photometric
KW  - galaxies: individual: LMC
KW  - Magellanic Clouds
Y1  - 2015
U6  - https://doi.org/10.1093/mnras/stv2054
SN  - 0035-8711
SN  - 1365-2966
VL  - 454
IS  - 1
SP  - 839
EP  - 848
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Piatti, Andres E.
A1  - de Grijs, Richard
A1  - Rubele, Stefano
A1  - Cioni, Maria-Rosa L.
A1  - Ripepi, Vincenzo
A1  - Kerber, Leandro
T1  - The VMC survey - XV. The Small Magellanic Cloud-Bridge connection history as traced by their star cluster populations
JF  - Monthly notices of the Royal Astronomical Society
N2  - We present results based on YJK(s) photometry of star clusters located in the outermost, eastern region of the Small Magellanic Cloud (SMC). We analysed a total of 51 catalogued clusters whose colour-magnitude diagrams (CMDs), having been cleaned from field-star contamination, were used to assess the clusters' reality and estimate ages of the genuine systems. Based on CMD analysis, 15 catalogued clusters were found to be possible non-genuine aggregates. We investigated the properties of 80 per cent of the catalogued clusters in this part of the SMC by enlarging our sample with previously obtained cluster ages, adopting a homogeneous scale for all. Their spatial distribution suggests that the oldest clusters, log(t yr(-1)) >= 9.6, are in general located at greater distances to the galaxy's centre than their younger counterparts - 9.0 <= log(t yr(-1)) <= 9.4 - while two excesses of clusters are seen at log(t yr(-1)) similar to 9.2 and log(t yr(-1)) similar to 9.7. We found a trail of younger clusters which follow the wing/bridge components. This long spatial sequence does not only harbour very young clusters, log(t yr(-1)) similar to 7.3, but it also hosts some of intermediate ages, log(t yr(-1)) similar to 9.1. The derived cluster and field-star formation frequencies as a function of age are different. The most surprising feature is an observed excess of clusters with ages of log(t yr(-1)) <9.0, which could have been induced by interactions with the LMC.
KW  - techniques: photometric
KW  - galaxies: individual: SMC
KW  - Magellanic Clouds
Y1  - 2015
U6  - https://doi.org/10.1093/mnras/stv635
SN  - 0035-8711
SN  - 1365-2966
VL  - 450
IS  - 1
SP  - 552
EP  - 563
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Pieplow, Gregor
A1  - Henkel, Carsten
T1  - Cherenkov friction on a neutral particle moving parallel to a dielectric
JF  - Journal of physics : Condensed matter
N2  - We describe a simple mechanism of quantum friction for a particle moving parallel to a dielectric, based on a fully relativistic framework and the assumption of local equilibrium. The Cherenkov effect explains how the bare ground state becomes globally unstable and how fluctuations of the electromagnetic field and the particle's dipole are converted into pairs of excitations. Modeling the particle as a silver nano-sphere, we investigate the spectrum of the force and its velocity dependence. We find that the damping of the plasmon resonance in the silver particle has a relatively strong impact near the Cherenkov threshold velocity. We also present an expansion of the friction force near the threshold velocity for both damped and undamped particles.
KW  - quantum friction
KW  - quantum electrodynamics
KW  - Cherenkov radiation
KW  - transition radiation
KW  - fluctuation forces
Y1  - 2015
U6  - https://doi.org/10.1088/0953-8984/27/21/214001
SN  - 0953-8984
SN  - 1361-648X
VL  - 27
IS  - 21
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Piersimoni, Fortunato
A1  - Schlesinger, Raphael
A1  - Benduhn, Johannes
A1  - Spoltore, Donato
A1  - Reiter, Sina
A1  - Lange, Ilja
A1  - Koch, Norbert
A1  - Vandewal, Koen
A1  - Neher, Dieter
T1  - Charge Transfer Absorption and Emission at ZnO/Organic Interfaces
JF  - The journal of physical chemistry letters
N2  - We investigate hybrid charge transfer states (HCTS) at the planar interface between a-NPD and ZnO by spectrally resolved electroluminescence (EL) and external quantum efficiency (EQE) measurements. Radiative decay of HCTSs is proven by distinct emission peaks in the EL spectra of such bilayer devices in the NIR at energies well below the bulk a-NPD or ZnO emission. The EQE spectra display low energy contributions clearly red-shifted with respect to the a-NPD photocurrent and partially overlapping with the EL emission. Tuning of the energy gap between the ZnO conduction band and a-NPD HOMO level (E-int) was achieved by modifying the ZnO surface with self-assembled monolayers based on phosphonic acids. We find a linear dependence of the peak position of the NIR EL on E-int, which unambiguously attributes the origin of this emission to radiative recombination between an electron on the ZnO and a hole on a-NPD. In accordance with this interpretation, we find a strictly linear relation between the open-circuit voltage and the energy of the charge state for such hybrid organicinorganic interfaces.
Y1  - 2015
U6  - https://doi.org/10.1021/jz502657z
SN  - 1948-7185
VL  - 6
IS  - 3
SP  - 500
EP  - 504
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Pietzsch, Annette
A1  - Hennies, Franz
A1  - Miedema, Piter S.
A1  - Kennedy, Brian
A1  - Schlappa, Justine
A1  - Schmitt, Thorsten
A1  - Strocov, Vladimir N.
A1  - Föhlisch, Alexander
T1  - Snapshots of the Fluctuating Hydrogen Bond Network in Liquid Water on the Sub-Femtosecond Timescale with Vibrational Resonant Inelastic x-ray Scattering
JF  - Physical review letters
N2  - Liquid water molecules interact strongly with each other, forming a fluctuating hydrogen bond network and thereby giving rise to the anomalous phase diagram of liquid water. Consequently, symmetric and asymmetric water molecules have been found in the picosecond time average with IR and optical Raman spectroscopy. With subnatural linewidth resonant inelastic x-ray scattering (RIXS) at vibrational resolution, we take sub-femtosecond snapshots of the electronic and structural properties of water molecules in the hydrogen bond network. We derive a strong dominance of nonsymmetric molecules in liquid water in contrast to the gas phase on the sub-femtosecond timescale of RIXS and determine the fraction of highly asymmetrically distorted molecules.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevLett.114.088302
SN  - 0031-9007
SN  - 1079-7114
VL  - 114
IS  - 8
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Pikovskij, Arkadij
T1  - First and second sound in disordered strongly nonlinear lattices: numerical study
JF  - Journal of statistical mechanics: theory and experiment
N2  - We study numerically secondary modes on top of a chaotic state in disordered nonlinear lattices. Two basic models are considered, with or without a local on-site potential. By performing periodic spatial modulation of displacement and kinetic energy, and following the temporal evolution of the corresponding spatial profiles, we reveal different modes which can be interpreted as first and second sound.
KW  - disordered systems (theory)
KW  - connections between chaos and statistical physics
Y1  - 2015
U6  - https://doi.org/10.1088/1742-5468/2015/08/P08007
SN  - 1742-5468
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Pikovskij, Arkadij
T1  - Maximizing Coherence of Oscillations by External Locking
JF  - Physical review letters
N2  - We study how coherence of noisy oscillations can be optimally enhanced by external locking. Based on the condition of minimizing the phase diffusion constant, we find the optimal forcing explicitly in the limits of small and large noise, in dependence of the phase sensitivity of the oscillator. We show analytically that the form of the optimal force bifurcates with the noise intensity; this is confirmed by the analysis of an optimal locking forcing for an experimentally obtained phase sensitivity of a neural cell. In the limit of small noise, the results are compared with purely deterministic conditions of optimal locking.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevLett.115.070602
SN  - 0031-9007
SN  - 1079-7114
VL  - 115
IS  - 7
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Pikovskij, Arkadij
A1  - Rosenblum, Michael
T1  - Dynamics of globally coupled oscillators: Progress and perspectives
JF  - Chaos : an interdisciplinary journal of nonlinear science
N2  - In this paper, we discuss recent progress in research of ensembles of mean field coupled oscillators. Without an ambition to present a comprehensive review, we outline most interesting from our viewpoint results and surprises, as well as interrelations between different approaches. (c) 2015 AIP Publishing LLC.
Y1  - 2015
U6  - https://doi.org/10.1063/1.4922971
SN  - 1054-1500
SN  - 1089-7682
VL  - 25
IS  - 9
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Pohl, Manuela
A1  - Wilhelm, Alina
A1  - Telezhinsky, Igor O.
T1  - Reacceleration of electrons in supernova remnants
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. radio spectra of many shell-type supernova remnants show deviations from those expected on theoretical grounds.
 Aims. In this paper we determine the effect of stochastic reacceleration on the spectra of electrons in the GeV band and at lower energies, and we investigate whether reacceleration can explain the observed variation in radio spectral indices.
 Methods. We explicitely calculated the momentum diffusion coefficient for 3 types of turbulence expected downstream of the forward shock: fast-mode waves, small-scale non-resonant modes, and large-scale modes arising from turbulent dynamo activity. After noting that low-energy particles are efficiently coupled to the quasi-thermal plasma, a simplified cosmic-ray transport equation can be formulated and is numerically solved.
 Results. Only fast-mode waves can provide momentum diffusion fast enough to significantly modify the spectra of particles. Using a synchrotron emissivity that accurately reflects a highly turbulent magnetic field, we calculated the radio spectral index and find that soft spectra with index a alpha less than or similar to -0.6 can be maintained over more than 2 decades in radio frequency, even if the electrons experience reacceleration for only one acceleration time. A spectral hardening is possible but considerably more frequency-dependent. The spectral modification imposed by stochastic reacceleration downstream of the forward shock depends only weakly on the initial spectrum provided by, e.g., diffusive shock acceleration at the shock itself.
KW  - acceleration of particles
KW  - turbulence
KW  - cosmic rays
KW  - ISM: supernova remnants
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201425027
SN  - 0004-6361
SN  - 1432-0746
VL  - 574
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Politi, Antonio
A1  - Rosenblum, Michael
T1  - Equivalence of phase-oscillator and integrate-and-fire models
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - A quantitative comparison of various classes of oscillators (integrate-and-fire, Winfree, and Kuramoto-Daido type) is performed in the weak-coupling limit for a fully connected network of identical units. An almost perfect agreement is found, with only tiny differences among the models. We also show that the regime of self-consistent partial synchronization is rather general and can be observed for arbitrarily small coupling strength in any model class. As a byproduct of our study, we are able to show that an integrate-and-fire model with a generic pulse shape can be always transformed into a similar model with delta pulses and a suitable phase response curve.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.91.042916
SN  - 1539-3755
SN  - 1550-2376
VL  - 91
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Premont-Schwarz, Mirabelle
A1  - Schreck, Simon
A1  - Iannuzzi, Marcella
A1  - Nibbering, Erik T. J.
A1  - Odelius, Michael
A1  - Wernet, Philippe
T1  - Correlating Infrared and X-ray Absorption Energies for Molecular-Level Insight into Hydrogen Bond Making and Breaking in Solution
JF  - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2  - While ubiquitous, the making and breaking of hydrogen bonds in solution is notoriously difficult to study due to the associated complex changes of nuclear and electronic structures. With the aim to reduce the according uncertainty in correlating experimental observables and hydrogen-bond configurations, we combine the information from proximate methods to study the N-H center dot center dot center dot O hydrogen bond in solution. We investigate hydrogen-bonding of the N-H group of N-methylaniline with oxygen from liquid DMSO and acetone with infrared spectra in the N-H stretching region and X-ray absorption spectra at the N K-edge. We experimentally observe blue shifts of the infrared stretching band and an X-ray absorption pre-edge peak when going from DMSO to acetone. With ab initio molecular dynamics simulations and calculated spectra, we qualitatively reproduce the experimental observables but we do not reach quantitative agreement with experiment. The infrared spectra support the notion of weakening the N-H center dot center dot center dot O hydrogen bond from DMSO to acetone. However, we fail to theoretically reproduce the measured shift of the X-ray absorption pre-edge peak. We discuss possible shortcomings of the simulation models and spectrum calculations. Common features and distinct differences with the O-H center dot center dot center dot O hydrogen bond are highlighted, and the implications for monitoring hydrogen-bond breaking in solution are discussed.
Y1  - 2015
U6  - https://doi.org/10.1021/acs.jpcb.5b02954
SN  - 1520-6106
VL  - 119
IS  - 25
SP  - 8115
EP  - 8124
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Pulkkinen, Otto
A1  - Metzler, Ralf
T1  - Variance-corrected Michaelis-Menten equation predicts transient rates of single-enzyme reactions and response times in bacterial gene-regulation
JF  - Scientific reports
N2  - Many chemical reactions in biological cells occur at very low concentrations of constituent molecules. Thus, transcriptional gene-regulation is often controlled by poorly expressed transcription-factors, such as E. coli lac repressor with few tens of copies. Here we study the effects of inherent concentration fluctuations of substrate-molecules on the seminal Michaelis-Menten scheme of biochemical reactions. We present a universal correction to the Michaelis-Menten equation for the reaction-rates. The relevance and validity of this correction for enzymatic reactions and intracellular gene-regulation is demonstrated. Our analytical theory and simulation results confirm that the proposed variance-corrected Michaelis-Menten equation predicts the rate of reactions with remarkable accuracy even in the presence of large non-equilibrium concentration fluctuations. The major advantage of our approach is that it involves only the mean and variance of the substrate-molecule concentration. Our theory is therefore accessible to experiments and not specific to the exact source of the concentration fluctuations.
Y1  - 2015
U6  - https://doi.org/10.1038/srep17820
SN  - 2045-2322
VL  - 5
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Pulkkinen, Otto
A1  - Metzler, Ralf
T1  - Variance-corrected Michaelis-Menten equation predicts transient rates of single-enzyme reactions and response times in bacterial gene-regulation
JF  - Scientific reports
N2  - Many chemical reactions in biological cells occur at very low concentrations of constituent molecules. Thus, transcriptional gene-regulation is often controlled by poorly expressed transcription-factors, such as E.coli lac repressor with few tens of copies. Here we study the effects of inherent concentration fluctuations of substrate-molecules on the seminal Michaelis-Menten scheme of biochemical reactions. We present a universal correction to the Michaelis-Menten equation for the reaction-rates. The relevance and validity of this correction for enzymatic reactions and intracellular gene-regulation is demonstrated. Our analytical theory and simulation results confirm that the proposed variance-corrected Michaelis-Menten equation predicts the rate of reactions with remarkable accuracy even in the presence of large non-equilibrium concentration fluctuations. The major advantage of our approach is that it involves only the mean and variance of the substrate-molecule concentration. Our theory is therefore accessible to experiments and not specific to the exact source of the concentration fluctuations.
Y1  - 2015
U6  - https://doi.org/10.1038/srep17820
SN  - 2045-2322
IS  - 5
PB  - Nature Publishing Group
CY  - London
ER  - 
TY  - JOUR
A1  - Raatz, Michael
A1  - Hintsche, Marius
A1  - Bahrs, Marco
A1  - Theves, Matthias
A1  - Beta, Carsten
T1  - Swimming patterns of a polarly flagellated bacterium in environments of increasing complexity
JF  - European physical journal special topics
N2  - The natural habitat of many bacterial swimmers is dominated by interfaces and narrow interstitial spacings where they frequently interact with the fluid boundaries in their vicinity. To quantify these interactions, we investigated the swimming behavior of the soil bacterium Pseudomonas putida in a variety of confined environments. Using microfluidic techniques, we fabricated structured microchannels with different configurations of cylindrical obstacles. In these environments, we analyzed the swimming trajectories for different obstacle densities and arrangements. Although the overall swimming pattern remained similar to movement in the bulk fluid, we observed a change in the turning angle distribution that could be attributed to collisions with the cylindrical obstacles. Furthermore, a comparison of the mean run length of the bacteria to the mean free path of a billiard particle in the same geometry indicated that, inside a densely packed environment, the trajectories of the bacterial swimmers are efficiently guided along the open spacings.
Y1  - 2015
U6  - https://doi.org/10.1140/epjst/e2015-02454-3
SN  - 1951-6355
SN  - 1951-6401
VL  - 224
IS  - 7
SP  - 1185
EP  - 1198
PB  - Springer
CY  - Heidelberg
ER  - 
TY  - JOUR
A1  - Reverey, Julia F.
A1  - Jeon, Jae-Hyung
A1  - Bao, Han
A1  - Leippe, Matthias
A1  - Metzler, Ralf
A1  - Selhuber-Unkel, Christine
T1  - Superdiffusion dominates intracellular particle motion in the supercrowded cytoplasm of pathogenic Acanthamoeba castellanii
JF  - Scientific reports
N2  - Acanthamoebae are free-living protists and human pathogens, whose cellular functions and pathogenicity strongly depend on the transport of intracellular vesicles and granules through the cytosol. Using high-speed live cell imaging in combination with single-particle tracking analysis, we show here that the motion of endogenous intracellular particles in the size range from a few hundred nanometers to several micrometers in Acanthamoeba castellanii is strongly superdiffusive and influenced by cell locomotion, cytoskeletal elements, and myosin II. We demonstrate that cell locomotion significantly contributes to intracellular particle motion, but is clearly not the only origin of superdiffusivity. By analyzing the contribution of microtubules, actin, and myosin II motors we show that myosin II is a major driving force of intracellular motion in A. castellanii. The cytoplasm of A. castellanii is supercrowded with intracellular vesicles and granules, such that significant intracellular motion can only be achieved by actively driven motion, while purely thermally driven diffusion is negligible.
Y1  - 2015
U6  - https://doi.org/10.1038/srep11690
SN  - 2045-2322
VL  - 5
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Richter, Philipp
A1  - de Boer, Klaas S.
A1  - Werner, Klaus
A1  - Rauch, Thomas
T1  - High-velocity gas toward the LMC resides in the Milky Way halo
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Aims. To explore the origin of high-velocity gas in the direction of the Large Magellanic Cloud, (LMC) we analyze absorption lines in the ultraviolet spectrum of a Galactic halo star that is located in front of the LMC at d = 9.2(-7.2)(+4.1) kpc distance.
 Methods. We study the velocity-component structure of low and intermediate metal ions (CII, SiII, SiIII) in the spectrum of RXJ0439.8-6809, as obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST), and measure equivalent widths and column densities for these ions. We supplement our COS data with a Far-Ultraviolet Spectroscopic Explorer (FUSE) spectrum of the nearby LMC star Sk-69 59 and with Hi 21 cm data from the Leiden-Argentina-Bonn (LAB) survey.
 Results. Metal absorption toward RXJ0439.8-6809 is unambiguously detected in three different velocity components near v(LSR) = 0, + 60, and + 150 km s(-1). The presence of absorption proves that all three gas components are situated in front of the star, thus located in the disk and inner halo of the Milky Way. For the high-velocity cloud (HVC) at v(LSR) = + 150 km s(-1), we derive an oxygen abundance of [O/H] = -0.63 (similar to 0.2 solar) from the neighboring Sk-69 59 sight line, in accordance with previous abundance measurements for this HVC. From the observed kinematics we infer that the HVC hardly participates in the Galactic rotation.
 Conclusions. Our study shows that the HVC toward the LMC represents a Milky Way halo cloud that traces low column density gas with relatively low metallicity. We rule out scenarios in which the HVC represents material close to the LMC that stems from a LMC outflow.
KW  - Galaxy: halo
KW  - Galaxy: evolution
KW  - ISM: abundances
KW  - ISM: structure
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201527451
SN  - 1432-0746
VL  - 584
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Roland, Steffen
A1  - Neubert, Sebastian
A1  - Albrecht, Steve
A1  - Stannowski, Bernd
A1  - Seger, Mark
A1  - Facchetti, Antonio
A1  - Schlatmann, Rutger
A1  - Rech, Bernd
A1  - Neher, Dieter
T1  - Hybrid Organic/Inorganic Thin-Film Multijunction Solar Cells Exceeding 11% Power Conversion Efficiency
JF  - Advanced materials
N2  - Hybrid multijunction solar cells comprising hydrogenated amorphous silicon and an organic bulk heterojunction are presented, reaching 11.7% power conversion efficiency. The benefits of merging inorganic and organic subcells are pointed out, the optimization of the cells, including optical modeling predictions and tuning of the recombination contact are described, and an outlook of this technique is given.
Y1  - 2015
U6  - https://doi.org/10.1002/adma.201404698
SN  - 0935-9648
SN  - 1521-4095
VL  - 27
IS  - 7
SP  - 1262
EP  - 1267
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Rosenblum, Michael
A1  - Pikovskij, Arkadij
T1  - Two types of quasiperiodic partial synchrony in oscillator ensembles
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We analyze quasiperiodic partially synchronous states in an ensemble of Stuart-Landau oscillators with global nonlinear coupling. We reveal two types of such dynamics: in the first case the time-averaged frequencies of oscillators and of the mean field differ, while in the second case they are equal, but the motion of oscillators is additionally modulated. We describe transitions from the synchronous state to both types of quasiperiodic dynamics, and a transition between two different quasiperiodic states. We present an example of a bifurcation diagram, where we show the borderlines for all these transitions, as well as domain of bistability.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.92.012919
SN  - 1539-3755
SN  - 1550-2376
VL  - 92
IS  - 1
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Rubensson, Jan-Erik
A1  - Soderstrom, Johan
A1  - Binggeli, Christian
A1  - Grasjo, Joakim
A1  - Andersson, Johan
A1  - Sathe, Conny
A1  - Hennies, Franz
A1  - Bisogni, Valentina
A1  - Huang, Yaobo
A1  - Olalde, Paul
A1  - Schmitt, Thorsten
A1  - Strocov, Vladimir N.
A1  - Föhlisch, Alexander
A1  - Kennedy, Brian
A1  - Pietzsch, Annette
T1  - Rydberg-Resolved Resonant Inelastic Soft X-Ray Scattering: Dynamics at Core Ionization Thresholds
JF  - Physical review letters
N2  - Resonant inelastic x-ray scattering spectra excited in the immediate vicinity of the core-level ionization thresholds of N-2 have been recorded. Final states of well-resolved symmetry-selected Rydberg series converging to valence-level ionization thresholds with vibrational excitations are observed. The results are well described by a quasi-two-step model which assumes that the excited electron is unaffected by the radiative decay. This threshold dynamics simplifies the interpretation of resonant inelastic x-ray scattering spectra considerably and facilitates characterization of low-energy excited final states in molecular systems.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevLett.114.133001
SN  - 0031-9007
SN  - 1079-7114
VL  - 114
IS  - 13
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Safdari, Hadiseh
A1  - Chechkin, Aleksei V.
A1  - Jafari, Gholamreza R.
A1  - Metzler, Ralf
T1  - Aging scaled Brownian motion
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - Scaled Brownian motion (SBM) is widely used to model anomalous diffusion of passive tracers in complex and biological systems. It is a highly nonstationary process governed by the Langevin equation for Brownian motion, however, with a power-law time dependence of the noise strength. Here we study the aging properties of SBM for both unconfined and confined motion. Specifically, we derive the ensemble and time averaged mean squared displacements and analyze their behavior in the regimes of weak, intermediate, and strong aging. A very rich behavior is revealed for confined aging SBM depending on different aging times and whether the process is sub- or superdiffusive. We demonstrate that the information on the aging factorizes with respect to the lag time and exhibits a functional form that is identical to the aging behavior of scale-free continuous time random walk processes. While SBM exhibits a disparity between ensemble and time averaged observables and is thus weakly nonergodic, strong aging is shown to effect a convergence of the ensemble and time averaged mean squared displacement. Finally, we derive the density of first passage times in the semi-infinite domain that features a crossover defined by the aging time.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.91.042107
SN  - 1539-3755
SN  - 1550-2376
VL  - 91
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Safdari, Hadiseh
A1  - Cherstvy, Andrey G.
A1  - Chechkin, Aleksei V.
A1  - Thiel, Felix
A1  - Sokolov, Igor M.
A1  - Metzler, Ralf
T1  - Quantifying the non-ergodicity of scaled Brownian motion
JF  - Journal of physics : A, Mathematical and theoretical
N2  - We examine the non-ergodic properties of scaled Brownian motion (SBM), a non-stationary stochastic process with a time dependent diffusivity of the form D(t) similar or equal to t(alpha-1). We compute the ergodicity breaking parameter EB in the entire range of scaling exponents a, both analytically and via extensive computer simulations of the stochastic Langevin equation. We demonstrate that in the limit of long trajectory lengths T and short lag times Delta the EB parameter as function of the scaling exponent a has no divergence at alpha - 1/2 and present the asymptotes for EB in different limits. We generalize the analytical and simulations results for the time averaged and ergodic properties of SBM in the presence of ageing, that is, when the observation of the system starts only a finite time span after its initiation. The approach developed here for the calculation of the higher time averaged moments of the particle displacement can be applied to derive the ergodic properties of other stochastic processes such as fractional Brownian motion.
KW  - scaled Brownian motion
KW  - anomalous diffusion
KW  - ageing
Y1  - 2015
U6  - https://doi.org/10.1088/1751-8113/48/37/375002
SN  - 1751-8113
SN  - 1751-8121
VL  - 48
IS  - 37
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Saleem, Hussam
A1  - Downey, Austin
A1  - Laflamme, Simon
A1  - Kollosche, Matthias
A1  - Ubertini, Filippo
T1  - Investigation of Dynamic Properties of a Novel Capacitive-based Sensing Skin for Nondestructive Testing
JF  - Materials evaluation
N2  - A capacitive-based soft elastomeric strain sensor was recently developed by the authors for structural health monitoring applications. Arranged in a network configuration, the sensor becomes a sensing skin, where local deformations can be monitored over a global area. The sensor transduces a change in geometry into a measurable change in capacitance, which can be converted into strain using a previously developed electromechanical model. Prior studies have demonstrated limitations of this electromechanical model for dynamic excitations beyond 15 Hz, because of a loss in linearity in the sensor's response. In this paper, the dynamic behavior beyond 15 Hz is further studied, and a new version of the electromechanical model is proposed to accommodate dynamic strain measurements up to 40 Hz. This behavior is characterized by subjecting the sensor to a frequency sweep and identifying possible sources of nonlinearities beyond 15 Hz. Results show possible frequency dependence of the materials' Poisson's ratios, which are successfully modeled and integrated into the electromechanical model. This demonstrates that the proposed sensor can be used for monitoring and evaluation of structural responses up to 40 Hz, a range covering the vast majority of the dominating frequency responses of civil infrastructures.
KW  - nondestructive testing
KW  - structural health monitoring
KW  - soft elastomeric capacitor
KW  - capacitive sensor
KW  - vibration monitoring
KW  - sensing skin
Y1  - 2015
SN  - 0025-5327
VL  - 73
IS  - 10
SP  - 1390
EP  - 1397
PB  - American Society for Nondestructive Testing
CY  - Columbus
ER  - 
TY  - JOUR
A1  - Sander, A.
A1  - Hamann, Wolf-Rainer
A1  - Hainich, Rainer
A1  - Shenar, Tomer
A1  - Todt, Helge Tobias
T1  - Hydrodynamic modeling of massive star atmospheres
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - In the last decades, stellar atmosphere codes have become a key tool in understanding massive stars, including precise calculations of stellar and wind parameters, such as temperature, massloss rate, and terminal wind velocity. Nevertheless, for these models the hydrodynamic equation is not solved in the wind. Motivated by the results of the CAK theory, the models typically use a beta velocity law, which however turns out not to be adequate for stars with very strong winds, and treat the mass-loss rate as a free parameter. In a new branch of the Potsdam Wolf-Rayet model atmosphere (PoWR) code, we solve the hydrodynamic equation consistently throughout the stellar atmosphere. The PoWR code performs the calculation of the radiative force without approximations (e.g. Sobolev). We show the impact of hydrodynamically consistent modelling on OB and WR stars in comparison to conventional models and discuss the obtained velocity fields and their impact on the observed spectral lines.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-87857
SP  - 139
EP  - 142
ER  - 
TY  - JOUR
A1  - Sander, Andreas Alexander Christoph
A1  - Shenar, Tomer
A1  - Hainich, Rainer
A1  - Gimenez-Garcia, Ana
A1  - Todt, Helge Tobias
A1  - Hamann, Wolf-Rainer
T1  - On the consistent treatment of the quasi-hydrostatic layers in hot star atmospheres
JF  - Astronomy and astrophysics : an international weekly journal
N2  - Context. Spectroscopic analysis remains the most common method to derive masses of massive stars, the most fundamental stellar parameter. While binary orbits and stellar pulsations can provide much sharper constraints on the stellar mass, these methods are only rarely applicable to massive stars. Unfortunately, spectroscopic masses of massive stars heavily depend on the detailed physics of model atmospheres.
 Aims. We demonstrate the impact of a consistent treatment of the radiative pressure on inferred gravities and spectroscopic masses of massive stars. Specifically, we investigate the contribution of line and continuum transitions to the photospheric radiative pressure. We further explore the effect of model parameters, e.g., abundances, on the deduced spectroscopic mass. Lastly, we compare our results with the plane-parallel TLUSTY code, commonly used for the analysis of massive stars with photospheric spectra.
 Methods. We calculate a small set of O-star models with the Potsdam Wolf-Rayet (PoWR) code using different approaches for the quasi-hydrostatic part. These models allow us to quantify the effect of accounting for the radiative pressure consistently. We further use PoWR models to show how the Doppler widths of line profiles and abundances of elements such as iron affect the radiative pressure, and, as a consequence, the derived spectroscopic masses.
 Results. Our study implies that errors on the order of a factor of two in the inferred spectroscopic mass are to be expected when neglecting the contribution of line and continuum transitions to the radiative acceleration in the photosphere. Usage of implausible microturbulent velocities, or the neglect of important opacity sources such as Fe, may result in errors of approximately 50% in the spectroscopic mass. A comparison with TLUSTY model atmospheres reveals a very good agreement with PoWR at the limit of low mass-loss rates.
KW  - stars: early-type
KW  - stars: mass-loss
KW  - stars: winds, outflows
KW  - stars: atmospheres
KW  - stars: fundamental parameters
KW  - stars: massive
Y1  - 2015
U6  - https://doi.org/10.1051/0004-6361/201425356
SN  - 0004-6361
SN  - 1432-0746
VL  - 577
PB  - EDP Sciences
CY  - Les Ulis
ER  - 
TY  - JOUR
A1  - Sandev, Trifce
A1  - Chechkin, Aleksei V.
A1  - Kantz, Holger
A1  - Metzler, Ralf
T1  - Diffusion and fokker-planck-smoluchowski equations with generalized memory kernel
JF  - Fractional calculus and applied analysis : an international journal for theory and applications
N2  - We consider anomalous stochastic processes based on the renewal continuous time random walk model with different forms for the probability density of waiting times between individual jumps. In the corresponding continuum limit we derive the generalized diffusion and Fokker-Planck-Smoluchowski equations with the corresponding memory kernels. We calculate the qth order moments in the unbiased and biased cases, and demonstrate that the generalized Einstein relation for the considered dynamics remains valid. The relaxation of modes in the case of an external harmonic potential and the convergence of the mean squared displacement to the thermal plateau are analyzed.
KW  - continuous time random walk (CTRW)
KW  - Fokker-Planck-Smoluchowski equation
KW  - Mittag-Leffler functions
KW  - anomalous diffusion
KW  - multi-scaling
Y1  - 2015
U6  - https://doi.org/10.1515/fca-2015-0059
SN  - 1311-0454
SN  - 1314-2224
VL  - 18
IS  - 4
SP  - 1006
EP  - 1038
PB  - De Gruyter
CY  - Berlin
ER  - 
TY  - JOUR
A1  - Sandev, Trifce
A1  - Chechkin, Aleksei V.
A1  - Korabel, Nickolay
A1  - Kantz, Holger
A1  - Sokolov, Igor M.
A1  - Metzler, Ralf
T1  - Distributed-order diffusion equations and multifractality: Models and solutions
JF  - Physical review : E, Statistical, nonlinear and soft matter physics
N2  - We study distributed-order time fractional diffusion equations characterized by multifractal memory kernels, in contrast to the simple power-law kernel of common time fractional diffusion equations. Based on the physical approach to anomalous diffusion provided by the seminal Scher-Montroll-Weiss continuous time random walk, we analyze both natural and modified-form distributed-order time fractional diffusion equations and compare the two approaches. The mean squared displacement is obtained and its limiting behavior analyzed. We derive the connection between the Wiener process, described by the conventional Langevin equation and the dynamics encoded by the distributed-order time fractional diffusion equation in terms of a generalized subordination of time. A detailed analysis of the multifractal properties of distributed-order diffusion equations is provided.
Y1  - 2015
U6  - https://doi.org/10.1103/PhysRevE.92.042117
SN  - 1539-3755
SN  - 1550-2376
VL  - 92
IS  - 4
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Sellberg, Jonas A.
A1  - McQueen, Trevor A.
A1  - Laksmono, Hartawan
A1  - Schreck, Simon
A1  - Beye, Martin
A1  - DePonte, Daniel P.
A1  - Kennedy, Brian
A1  - Nordlund, Dennis
A1  - Sierra, Raymond G.
A1  - Schlesinger, Daniel
A1  - Tokushima, Takashi
A1  - Zhovtobriukh, Iurii
A1  - Eckert, Sebastian
A1  - Segtnan, Vegard H.
A1  - Ogasawara, Hirohito
A1  - Kubicek, Katharina
A1  - Techert, Simone
A1  - Bergmann, Uwe
A1  - Dakovski, Georgi L.
A1  - Schlotter, William F.
A1  - Harada, Yoshihisa
A1  - Bogan, Michael J.
A1  - Wernet, Philippe
A1  - Föhlisch, Alexander
A1  - Pettersson, Lars G. M.
A1  - Nilsson, Anders
T1  - X-ray emission spectroscopy of bulk liquid water in "no-man's land"
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - The structure of bulk liquid water was recently probed by x-ray scattering below the temperature limit of homogeneous nucleation (T-H) of similar to 232 K [J. A. Sellberg et al., Nature 510, 381-384 (2014)]. Here, we utilize a similar approach to study the structure of bulk liquid water below T-H using oxygen K-edge x-ray emission spectroscopy (XES). Based on previous XES experiments [T. Tokushima et al., Chem. Phys. Lett. 460, 387-400 (2008)] at higher temperatures, we expected the ratio of the 1b(1)' and 1b(1)" peaks associated with the lone-pair orbital in water to change strongly upon deep supercooling as the coordination of the hydrogen (H-) bonds becomes tetrahedral. In contrast, we observed only minor changes in the lone-pair spectral region, challenging an interpretation in terms of two interconverting species. A number of alternative hypotheses to explain the results are put forward and discussed. Although the spectra can be explained by various contributions from these hypotheses, we here emphasize the interpretation that the line shape of each component changes dramatically when approaching lower temperatures, where, in particular, the peak assigned to the proposed disordered component would become more symmetrical as vibrational interference becomes more important. (C) 2015 AIP Publishing LLC.
Y1  - 2015
U6  - https://doi.org/10.1063/1.4905603
SN  - 0021-9606
SN  - 1089-7690
VL  - 142
IS  - 4
PB  - American Institute of Physics
CY  - Melville
ER  - 
TY  - JOUR
A1  - Shenar, Tomer
A1  - Hamann, Wolf-Rainer
A1  - Todt, Helge Tobias
T1  - The impact of rotation on the line profiles of Wolf-Rayet stars
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - The distribution of angular momentum in massive stars is a critical component of their evolution, yet not much is known on the rotation velocities of Wolf-Rayet stars. There are various indications that rapidly rotating Wolf-Rayet stars should exist. Unfortunately, due to their expanding atmospheres, rotational velocities of Wolf-Rayet stars are very difficult to measure. In this work, we model the effects of rotation on the atmospheres of Wolf-Rayet stars by implementing a 3D integration scheme in the PoWR code. We further investigate whether the peculiar spectra of five Wolf-Rayet stars may imply rapid rotation, infer the corresponding rotation parameters, and discuss the implications of our results. We find that rotation helps to reproduce the unique spectra analyzed here. However, if rotation is indeed involved, the inferred rotational velocities at the stellar surface are large (∼ 200 km/s), and the implied co-rotation radii (∼ 10R∗) suggest the existence of very strong photospheric magnetic fields (∼ 20 kG).
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88008
SP  - 193
EP  - 196
ER  - 
TY  - JOUR
A1  - Shenar, Tomer
A1  - Oskinova, Lida
A1  - Hamann, Wolf-Rainer
A1  - Corcoran, Michael F.
A1  - Moffat, Anthony F. J.
A1  - Pablo, Herbert
A1  - Richardson, Noel D.
A1  - Waldron, Wayne L.
A1  - Huenemoerder, David P.
A1  - Maiz Apellaniz, Jesus
A1  - Nichols, Joy S.
A1  - Todt, Helge Tobias
A1  - Naze, Yael
A1  - Hoffman, Jennifer L.
A1  - Pollock, Andy M. T.
A1  - Negueruela, Ignacio
T1  - A coordinated X-Ray and optical campaign of the nearest massive eclipsing binary, delta ORIONIS Aa. IV. A multiwavelength, non-lte spectroscopic analysis
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - Eclipsing systems of massive stars allow one to explore the properties of their components in great detail. We perform a multi-wavelength, non-LTE analysis of the three components of the massive multiple system delta Ori A, focusing on the fundamental stellar properties, stellar winds, and X-ray characteristics of the system. The primary's distance-independent parameters turn out to be characteristic for its spectral type (O9.5 II), but usage of the Hipparcos parallax yields surprisingly low values for the mass, radius, and luminosity. Consistent values follow only if delta Ori lies at about twice the Hipparcos distance, in the vicinity of the sigma-Orionis cluster. The primary and tertiary dominate the spectrum and leave the secondary only marginally detectable. We estimate the V-band magnitude difference between primary and secondary to be Delta V approximate to 2.(m)8. The inferred parameters suggest that the secondary is an early B-type dwarf (approximate to B1 V), while the tertiary is an early B-type subgiant (approximate to B0 IV). We find evidence for rapid turbulent velocities (similar to 200 km s(-1)) and wind inhomogeneities, partially optically thick, in the primary's wind. The bulk of the X-ray emission likely emerges from the primary's stellar wind (logL(X)/L-Bol approximate to -6.85), initiating close to the stellar surface at R-0 similar to 1.1 R-*. Accounting for clumping, the mass-loss rate of the primary is found to be log (M) over dot approximate to -6.4 (M-circle dot yr(-1))., which agrees with hydrodynamic predictions, and provides a consistent picture along the X-ray, UV, optical, and radio spectral domains.
KW  - binaries: close
KW  - binaries: eclipsing
KW  - stars: early-type
KW  - stars: individual ([HD 36486]delta Ori A)
KW  - X-rays: stars
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/809/2/135
SN  - 0004-637X
SN  - 1538-4357
VL  - 809
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Shin, Jaeoh
A1  - Cherstvy, Andrey G.
A1  - Kim, Won Kyu
A1  - Metzler, Ralf
T1  - Facilitation of polymer looping and giant polymer diffusivity in crowded solutions of active particles
JF  - New journal of physics : the open-access journal for physics
N2  - We study the dynamics of polymer chains in a bath of self-propelled particles (SPP) by extensive Langevin dynamics simulations in a two-dimensional model system. Specifically, we analyse the polymer looping properties versus the SPP activity and investigate how the presence of the active particles alters the chain conformational statistics. We find that SPPs tend to extend flexible polymer chains, while they rather compactify stiffer semiflexible polymers, in agreement with previous results. Here we show that higher activities of SPPs yield a higher effective temperature of the bath and thus facilitate the looping kinetics of a passive polymer chain. We explicitly compute the looping probability and looping time in a wide range of the model parameters. We also analyse the motion of a monomeric tracer particle and the polymer's centre of mass in the presence of the active particles in terms of the time averaged mean squared displacement, revealing a giant diffusivity enhancement for the polymer chain via SPP pooling. Our results are applicable to rationalising the dimensions and looping kinetics of biopolymers at constantly fluctuating and often actively driven conditions inside biological cells or in suspensions of active colloidal particles or bacteria cells.
KW  - diffusion
KW  - active transport
KW  - polymers
Y1  - 2015
U6  - https://doi.org/10.1088/1367-2630/17/11/113008
SN  - 1367-2630
VL  - 17
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Shin, Jaeoh
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
T1  - Self-subdiffusion in solutions of star-shaped crowders: non-monotonic effects of inter-particle interactions
JF  - New journal of physics : the open-access journal for physics
N2  - We examine by extensive computer simulations the self-diffusion of anisotropic star-like particles in crowded two-dimensional solutions. We investigate the implications of the area coverage fraction phi of the crowders and the crowder-crowder adhesion properties on the regime of transient anomalous diffusion. We systematically compute the mean squared displacement (MSD) of the particles, their time averaged MSD, and the effective diffusion coefficient. The diffusion is ergodic in the limit of long traces, such that the mean time averaged MSD converges towards the ensemble averaged MSD, and features a small residual amplitude spread of the time averaged MSD from individual trajectories. At intermediate time scales, we quantify the anomalous diffusion in the system. Also, we show that the translational-but not rotational-diffusivity of the particles Dis a nonmonotonic function of the attraction strength between them. Both diffusion coefficients decrease as the power law D(phi) similar to (1 - phi/phi*)(2 ... 2.4) with the area fraction phi occupied by the crowders and the critical value phi*. Our results might be applicable to rationalising the experimental observations of non-Brownian diffusion for a number of standard macromolecular crowders used in vitro to mimic the cytoplasmic conditions of living cells.
KW  - anomalous diffusion
KW  - crowded fluids
KW  - stochastic processes
Y1  - 2015
U6  - https://doi.org/10.1088/1367-2630/17/11/113028
SN  - 1367-2630
VL  - 17
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Shin, Jaeoh
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
T1  - Kinetics of polymer looping with macromolecular crowding: effects of volume fraction and crowder size
JF  - Soft matter
N2  - The looping of polymers such as DNA is a fundamental process in the molecular biology of living cells, whose interior is characterised by a high degree of molecular crowding. We here investigate in detail the looping dynamics of flexible polymer chains in the presence of different degrees of crowding. From the analysis of the looping-unlooping rates and the looping probabilities of the chain ends we show that the presence of small crowders typically slows down the chain dynamics but larger crowders may in fact facilitate the looping. We rationalise these non-trivial and often counterintuitive effects of the crowder size on the looping kinetics in terms of an effective solution viscosity and standard excluded volume. It is shown that for small crowders the effect of an increased viscosity dominates, while for big crowders we argue that confinement effects (caging) prevail. The tradeoff between both trends can thus result in the impediment or facilitation of polymer looping, depending on the crowder size. We also examine how the crowding volume fraction, chain length, and the attraction strength of the contact groups of the polymer chain affect the looping kinetics and hairpin formation dynamics. Our results are relevant for DNA looping in the absence and presence of protein mediation, DNA hairpin formation, RNA folding, and the folding of polypeptide chains under biologically relevant high-crowding conditions.
Y1  - 2015
U6  - https://doi.org/10.1039/c4sm02007c
SN  - 1744-683X
SN  - 1744-6848
VL  - 11
IS  - 3
SP  - 472
EP  - 488
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Shin, Jaeoh
A1  - Cherstvy, Andrey G.
A1  - Metzler, Ralf
T1  - Polymer looping is controlled by macromolecular crowding, spatial confinement, and chain stiffness
JF  - ACS Macro Letters
N2  - We study by extensive computer simulations the looping characteristics of linear polymers with varying persistence length inside a spherical cavity in the presence of macromolecular crowding. For stiff chains, the looping probability and looping time reveal wildly oscillating patterns as functions of the chain length. The effects of crowding differ dramatically for flexible versus stiff polymers. While for flexible chains the looping kinetics is slowed down by the crowders, for stiffer chains the kinetics turns out to be either decreased or facilitated, depending on the polymer length. For severe confinement, the looping kinetics may become strongly facilitated by crowding. Our findings are of broad impact for DNA looping in the crowded and compartmentalized interior of living biological cells.
Y1  - 2015
U6  - https://doi.org/10.1021/mz500709w
SN  - 2161-1653
VL  - 4
IS  - 2
SP  - 202
EP  - 206
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Shrader, C. R.
A1  - Hamaguchi, K.
A1  - Sturner, Steven J.
A1  - Oskinova, Lida
A1  - Almeyda, T.
A1  - Petre, R.
T1  - Hifg-energy properties of the enigmatic be STAR gamma Cassiopeiae
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics
N2  - We present the results of a broadband X-ray study of the enigmatic Be star Gamma Cassiopeiae (herein gamma Cas) based on observations made with both the Suzaku and INTEGRAL observatories.. Cas has long been recognized as the prototypical example of a small subclass of Be stars with moderately strong X-ray emission dominated by a hot thermal component in the 0.5-12 keV energy range (L-x approximate to 10(32)-10(33) erg s(-1)). This places them at the high end of the known luminosity distribution for stellar emission, but several orders of magnitude below typical accretion-powered Be X-ray binaries. The INTEGRAL observations spanned an eight-year baseline and represent the deepest measurement to date at energies above similar to 50 keV. We find that the INTEGRAL data are consistent within statistics to a constant intensity source above 20 keV, with emission extending up to similar to 100 keV, and that searches for all of the previously reported periodicities of the system at lower energies led to null results. We further find that our combined Suzaku and INTEGRAL spectrum, which we suggest is the most accurate broadband X-ray measurement of gamma Cas to date, is fitted extremely well with a thermal plasma emission model with a single absorption component. We found no compelling need for an additional non-thermal high-energy component. We discuss these results in the context of a currently favored models for gamma Cas and its analogs.
KW  - gamma rays: stars
KW  - stars: emission-line, Be
KW  - stars: individual (gamma Cassiopeiae)
KW  - white dwarfs
KW  - X-rays: binaries
KW  - X-rays: stars
Y1  - 2015
U6  - https://doi.org/10.1088/0004-637X/799/1/84
SN  - 0004-637X
SN  - 1538-4357
VL  - 799
IS  - 1
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Sillmann, Jana
A1  - Lenton, Timothy M.
A1  - Levermann, Anders
A1  - Ott, Konrad
A1  - Hulme, Mike
A1  - Benduhn, Francois
A1  - Horton, Joshua B.
T1  - COMMENTARY: No emergency argument for climate engineering
JF  - Nature climate change
Y1  - 2015
SN  - 1758-678X
SN  - 1758-6798
VL  - 5
IS  - 4
SP  - 290
EP  - 292
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Singh, Rajeev
A1  - Mellinger, Axel
T1  - Measurement of through-thickness thermal diffusivity of thermoplastics using thermal wave method
JF  - Indian journal of physics
N2  - Thermo-physical properties, such as thermal conductivity, thermal diffusivity and specific heat are important quantities that are needed to interpret and characterize thermoplastic materials. Such characterization is necessary for many applications, ranging from aerospace engineering to food packaging, electrical and electronic industry and medical science. In this work, the thermal diffusivity of commercially available polymeric films is measured in the thickness direction at room temperature using thermal wave method. The results obtained with this method are in good agreement with theoretical and experimental values.
KW  - Thermoplastics
KW  - Thermal diffusivity
KW  - Thermal wave method
KW  - Polymer
Y1  - 2015
U6  - https://doi.org/10.1007/s12648-014-0579-2
SN  - 0973-1458
SN  - 0974-9845
VL  - 89
IS  - 4
SP  - 361
EP  - 368
PB  - Indian Association for the Cultivation of Science
CY  - Kolkata
ER  - 
TY  - JOUR
A1  - Steinke, M.
A1  - Oskinova, Lida
A1  - Hamann, Wolf-Rainer
A1  - Sander, A.
T1  - The Wolf-Rayet stars WR102c and 102ka and their isolation
JF  - Wolf-Rayet Stars : Proceedings of an International Workshop held in Potsdam, Germany, 1.–5. June 2015
N2  - While the majority of very massive stars is clearly found in clusters, there are also very massive objects not associated with any cluster, suggesting they may have been born in isolation. In order to gain more insights, we studied the regions around two WR stars in the Galactic Center region. To understand the nature of the potential cluster around massive stars, photometry alone is not sufficient. We therefore used the ESO VLT/SINFONI integral field spectrograph to obtain photometry and spectra for the whole region around our two candidate stars. In total, more than 60 stars have been found and assigned a spectral type.
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-88503
SP  - 365
ER  -