cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
Quantitative modeling of the annealing-induced changes of the magnetotransport in Ga1−xMnxAs alloys
Creators: name: Michel, C.
name: Baranovskii, S. D
name: Thomas, P.
name: Heimbrodt, W.
name: Elm, M. T.
name: Klar, P. J.
name: Goldlücke, B.
name: Wurstbauer, Ursula
name: Reinwald, Matthias
name: Wegscheider, Werner
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: annealing, electronic density of states, gallium arsenide, gallium compounds, III-V semiconductors, magnetoresistance, manganese compounds, paramagnetic materials, semimagnetic semiconductors, Zeeman effect
subject: 530 Physik
subject: 72.20.My; 72.80.Ey; 75.50.Pp; 75.20.Ck

description: We study the changes of magnetoresistance induced by controlled thermal annealing at temperatures ranging from 300 to 600 °C of a Ga0.98Mn0.02As alloy grown by low-temperature molecular beam epitaxy. We use a resistor-network model for describing the electrical transport as a function of temperature and external magnetic field. The model is founded on classical semiconductor band transport and neglects many-body interactions. The peculiarities of dilute magnetic semiconductors, in particular, the magnetic-field induced changes of the density of states and the potential fluctuations due to the giant Zeeman splitting in the paramagnetic phase as well as spontaneous magnetization effects in the ferromagnetic phase, are accounted for in a mean-field fashion. This empirical transport model based on reasonable assumptions and realistic material parameters yields a satisfactory quantitative description of the experimentally obtained temperature and magnetic-field dependence of the resistivity of the entire series of annealed Ga0.98Mn0.02As samples, which exhibit metallic, semiconducting, and almost insulating transport behavior with increasing annealing temperature. Our analysis provides further understanding of the annealing-induced changes of the transport properties in dilute magnetic III-Mn-V semiconductors.
The mediated exploration of complex digital interaction design
Creators: name: Roast, Chris
name: Uruchurtu, Elizabeth
Publisher: name: SHU Research Data Archive (SHURDA)
Year: 2019
Subjects: Cognitive Dimensions, Interaction Design, Complex Interaction

description: This instrument is for use in facilitating formative assessments and insights of existing or envisaged complex interactive systems. By complex interactive systems, we mean systems where the idea of direct manipulation is inappropriate due to the presence of intermediate interactive notations designed for manipulating domain information.   The instrument was initially motivated by operational interpretations of the Cognitive Dimensions framework (Green, 1998; Blackwell, et al. 2001, Blackwell and Green 2000), and subsequent validation work (Roast and Khazaei, 2006) and experiences of applying the approach (Roast et al., 2013).  References  Blackwell, A.F., Britton, C., Cox, A. Green, T.R.G., Gurr, C.A., Kadoda, G.F., Kutar, M., Loomes, M., Nehaniv, C.L., Petre, M., Roast, C., Roes, C., Wong, A. and Young, R.M. (2001). Cognitive Dimensions of Notations: Design tools for cognitive technology. In M. Beynon, C.L. Nehaniv, and K. Dautenhahn (Eds.) Cognitive Technology 2001 (LNAI 2117). Springer-Verlag, pp. 325-341.   Blackwell, A.F. & Green, T.R.G. (2000). A Cognitive Dimensions Questionnaire optimised for users. In A.F. Blackwell & E. Bilotta (Eds.) Proceedings of the Twelth Annual Meeting of the Psychology of Programming Interest Group , 137-152.  Green, T. R. G. (1989). Cognitive dimensions of notations. In People and Computers V, A Sutcliffe and L Macaulay (Ed.) Cambridge University Press: Cambridge, pp. 443-460.  Roast, C. and Khazaei, B., An Investigation into the validation of formalised Cognitive Dimensions Design, Specification and Verification of Interactive Systems (DSVIS), July 2006, Springer Verlag.   Roast, C., Dearden, A. and Uruchurtu, E. (2013) Formative evaluation for complex interactive systems. In:Proceedings of the 6th Latin American Conference on Human Computer Interaction (CLIHC 2013), Springer Verlag.
U.P. Men Garanin Daridrata Ka Vartman SwaroopDaridra Vyaktiyon Kee SamasyayenDr. NEETU SINGH TOMAR, Post Doctoral Fellow, University Grant Commission New Delhi
Creators: name: Tomar, Neetusingh
Publisher: name: figshare
Year: 2021
Subjects: subject: Sociology
subject: FOS: Sociology

description: U.P. Men Garanin Daridrata Ka Vartman Swaroop
Current-induced heating in quantum well and quantum wire intersubband emitter structures
Creators: name: Herrle, Thomas
name: Haneder, Stephan
name: Tranitz, Hans-Peter
name: Reinwald, Matthias
name: Wegscheider, Werner
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: aluminium compounds, gallium arsenide, III-V semiconductors, photoluminescence, semiconductor quantum wells, semiconductor quantum wires
subject: 530 Physik
subject: 73.63.Hs; 73.63.Kv; 78.67.De; 78.67.Hc; 78.55.Cr

description: We discuss the influence of current-induced heating on the current-voltage (I-V) characteristics and the spectral behavior in quantum well and quantum wire intersubband emitter structures. A conventional quantum cascade laser structure in the AlGaAs/GaAs material system with undoped cladding layers and an undoped active region is examined. This heterostructure serves as a first growth step for quantum wire intersubband emitters fabricated by the cleaved-edge overgrowth technique. We discuss the influence of electrons supplied by a remote delta-silicon doping. Duty-cycle dependent measurements on the quantum wire structures confirm the influence of current-induced heating on the I-V characteristics as well as on the emission spectra.
Influence of electron-acoustic phonon scattering on off-resonant cavity feeding within a strongly coupled quantum-dot cavity system
Creators: name: Hughes, S.
name: Yao, P.
name: Milde, F.
name: Knorr, A.
name: Dalacu, D.
name: Mnaymneh, K.
name: Sazonova, V.
name: Poole, P. J.
name: Aers, G. C.
name: Lapointe, J.
name: Cheriton, R.
name: Williams, R. L.
Publisher: name: arXiv
Year: 2011
Subjects: subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: FOS: Physical sciences

description: We present a medium-dependent quantum optics approach to describe the influence of electron-acoustic phonon coupling on the emission spectra of a strongly coupled quantum-dot cavity system. Using a canonical Hamiltonian for light quantization and a photon Green function formalism, phonons are included to all orders through the dot polarizability function obtained within the independent Boson model. We derive simple user-friendly analytical expressions for the linear quantum light spectrum, including the influence from both exciton and cavity-emission decay channels. In the regime of semiconductor cavity-QED, we study cavity emission for various exciton-cavity detunings and demonstrate rich spectral asymmetries as well as cavity-mode suppression and enhancement effects. Our technique is nonperturbative, and non-Markovian, and can be applied to study photon emission from a wide range of semiconductor quantum dot structures, including waveguides and coupled cavity arrays. We compare our theory directly to recent and apparently puzzling experimental data for a single site-controlled quantum dot in a photonic crystal cavity and show good agreement as a function of cavity-dot detuning and as a function of temperature.
description: Regular Paper, Submitted to PRB, Dec, 2010
title: Epithelial transport of ions in health and disease: Leopoldina-Symposium, Halle/Saale, March 19 to 22, 2003
Creators: name: :None
Publisher: name: Wissenschaftliche Verlagsgesellschaft Stuttgart
Year: 2004
Subjects: subject: Ionentransport
subject: Physiologische Chemie
subject: 570

description: Nova Acta Leopoldina: NAL ; Abhandlungen der Deutschen Akademie der Naturforscher Leopoldina, vol. 89, Nummer 336
Source Mechanism of Long Period events recorded by a high density seismic network during the 2008 eruption on Mt Etna
Creators: name: De Barros, Louis
name: Lokmer, Ivan
name: Bean, C. J.
name: O'Brien, Gareth
name: Saccorotti, Gilberto
name: Métaxian, J. -P.
name: Zucarello, Luciano
name: Patanè, Domenico
Publisher: name: arXiv
Year: 2010
Subjects: subject: Geophysics (physics.geo-ph)
subject: FOS: Physical sciences

description: 129 Long Period (LP) events, divided into two families of similar events, were recorded by the 50 stations deployed on Mount Etna in the second half of June 2008. During this period lava was flowing from a lateral fracture after a summit strombolian eruption. In order to understand the mechanisms of these events, we perform moment tensor inversions. Inversions are initially kept unconstrained to estimate the most likely mechanism. Numerical tests show that unconstrained inversion leads to reliable moment tensor solutions because of the close proximity of numerous stations to the source positions. However, single forces cannot be accurately determined as they are very sensitive to uncertainties in the velocity model. Constrained inversions for a crack, a pipe or an explosion then allow us to accurately determine the structural orientations of the source mechanisms. Both numerical tests and LP event inversions emphasise the importance of using stations located as close as possible to the source. Inversions for both families show mechanisms with a strong volumetric component. These events are most likely generated by cracks striking SW-NE for both families and dipping 70°SE (Family 1) and 50°NW (Family 2). For Family 1 events, the crack geometry is nearly orthogonal to the dike-like structure along which events are located, while for Family 2 the location gave two pipe-like bodies which belong to the same plane as the crack mechanism. The orientations of the cracks are consistent with local tectonics, which shows a SW-NE weakness direction. The LP events appear to be a response to the lava fountain occurring on the 10th of May, 2008 as opposed to the flank lava flow.
KANPUR PARIKSHETRA KE KSHATRIYON KAA VARTMAN SWAROOPDaridra Vyaktiyon Kee Samasyayen
Creators: name: Tomar, Neetusingh
Publisher: name: figshare
Year: 2019
Subjects: subject: Sociology
subject: FOS: Sociology

description: KANPUR PARIKSHETRA KE KSHATRIYON KAA VARTMAN SWAROOP
U.P. Men Garanin Daridrata Ka Vartman SwaroopDaridra Vyaktiyon Kee Samasyayen
Creators: name: Tomar, Neetusingh
Publisher: name: figshare
Year: 2019
Subjects: subject: Sociology
subject: FOS: Sociology

description: U.P. Men Garanin Daridrata Ka Vartman Swaroop
Weak Localization in Ferromagnetic (Ga,Mn)As Nanostructures
Creators: name: Neumaier, Daniel
name: Wagner, Konrad
name: Geißler, Stefan
name: Wurstbauer, Ursula
name: Sadowski, Janusz
name: Wegscheider, Werner
name: Weiss, Dieter
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: 530 Physik
subject: 73.43.Jn, 72.25.Dc, 73.43.Qt

description: We report on the observation of weak localization in arrays of (Ga,Mn)As nanowires at millikelvin temperatures. The corresponding phase coherence length Lϕ is typically between 100 and 200 nm at 20 mK. Strong spin-orbit interaction in the material is manifested by a weak antilocalization correction around zero magnetic field.
Complete spectral gap in coupled dielectric waveguides embedded into metal
Creators: name: Liu, Wei
name: Sukhorukov, Andrey
name: Miroshnichenko, Andrey
name: Poulton, Chris
name: Xu, Zhiyong
name: Neshev, Dragomir
name: Kivshar, Yuri
Publisher: name: arXiv
Year: 2010
Subjects: subject: Optics (physics.optics)
subject: FOS: Physical sciences

description: We study a plasmonic coupler involving backward (TM_01) and forward (HE_11) modes of dielectric waveguides embedded into infinite metal. The simultaneously achievable contradirectional energy flows and codirectional wavevectors in different channels lead to a spectral gap, despite the absence of periodic structures along the waveguide. We demonstrate that a complete spectral gap can be achieved in a symmetric structure composed of four coupled waveguides.
description: 3 pages, 4 figures
'I feel out of place' : children born into the Lord's Resistance Army and the politics of belonging
Creators: name: Stewart, Beth W.
Publisher: name: University of British Columbia
Year: 2018

description: In the aftermath of nearly three decades of conflict in northern Uganda, children born into the rebel group the Lord’s Resistance Army (LRA) experience social, economic, and political exclusion. Thousands were born to mothers and often fathers who were abducted by the LRA and forced to marry inside the rebel group. The children are part of a global population of people born of sexual violence in conflict. This dissertation contributes to the small but growing body of work on this population called ‘children born of war.’ Using a child-centered methodology, this study is grounded in the everyday experiences of 29 children born into the LRA, with data collected at various points over a period of eight months between 2011 and 2016 in northern Uganda. The following research questions guided my inquiry: 1) How do the children experience their everyday social lives? 2) How do they make sense of their experiences? 3) What strategies and resources do they use or access to help navigate their everyday lives? 4) What macro and micro processes lend insight into or explain these experiences? To answer these questions, I developed a conceptual framework consisting of the ideas of a) the politics of belonging, inclusive of place-based, and b) nation-building and hegemonic masculinity. The findings point to the role of place-making in shaping the children’s social experiences. Careful examination of their everyday lives reveals the children’s efforts to negotiate the boundaries of their exclusion in effort to navigate toward better positions in life. Through drawings, journals, storytelling, and play, I interpret how the children make sense of their experiences and construct a sense of legitimacy despite their marginalization. By situating their experiences within current and historical political forces, their everyday experiences become intelligible as central to a local and national politics of belonging.
Aparaadh Nyay Aur Dand Ka Vartman SwaroopDaridra Vyaktiyon Kee Samasyayen
Creators: name: Tomar, Neetusingh
Publisher: name: figshare
Year: 2019
Subjects: subject: Sociology
subject: FOS: Sociology

description: Aparaadh Nyay Aur Dand Ka Vartman Swaroop
Detection of large magnetoanisotropy of electron spin dephasing in a high-mobility two-dimensional electron system in a [001] GaAs∕AlxGa1−xAs quantum well
Creators: name: Stich, Dominik
name: Jiang, J. H.
name: Korn, Tobias
name: Schulz, Robert
name: Schuh, Dieter
name: Wegscheider, Werner
name: Wu, M. W.
name: Schüller, Christian
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: 530 Physik
subject: 73.20.−r, 85.75.−d, 71.70.Ej

description: In time-resolved Faraday rotation experiments, we have detected an in-plane anisotropy of the electron spin-dephasing time (SDT) in an n-modulation-doped GaAs∕Al0.3Ga0.7As single quantum well. The SDT was measured with magnetic fields of B⩽1 T, applied in the [110] and [11̅ 0] in-plane crystal directions of the GaAs quantum well. For fields along [11̅ 0], we have found up to a factor of about 2 larger SDT than in the perpendicular direction. The observed SDTs also show strong anisotropic magnetic-field dependence. Fully microscopic calculations, by numerically solving the kinetic spin Bloch equations considering the D’yakonov-Perel’ and the Bir-Aronov-Pikus mechanisms, reproduce the experimental findings quantitatively. This quantitative analysis of the data allowed us to determine the relative strengths of Rashba and Dresselhaus terms in our sample. Moreover, we could predict the SDT for spins aligned in the [110] in-plane direction to be on the order of several nanoseconds, which is up to 2 orders of magnitude larger than that in the perpendicular in-plane direction.
High speed imaging of traveling waves in a granular material during silo discharge
Creators: name: Borzsonyi, Tamas
name: Kovacs, Zsolt
Publisher: name: arXiv
Year: 2011
Subjects: subject: Soft Condensed Matter (cond-mat.soft)
subject: FOS: Physical sciences

description: We report experimental observations of sound waves in a granular material during resonant silo discharge called silo music. The grain motion was tracked by high speed imaging while the resonance of the silo was detected by accelerometers and acoustic methods. The grains do not oscillate in phase at neighboring vertical locations, but information propagates upward in this system in the form of sound waves. We show that the wave velocity is not constant throughout the silo, but considerably increases towards the lower end of the system, suggesting increased pressure in this region, where the flow changes from cylindrical to converging flow. In the upper part of the silo the wave velocity matches the sound velocity measured in the same material when standing (in the absence of flow). Grain oscillations show a stick-slip character only in the upper part of the silo.
description: 5 pages, 5 figures, accepted to Phys. Rev. E
Dependence of spin dephasing on initial spin polarization in a high-mobility two-dimensional electron system
Creators: name: Stich, Dominik
name: Zhou, J.
name: Korn, Tobias
name: Schulz, Robert
name: Schuh, Dieter
name: Wegscheider, Werner
name: Wu, M. W.
name: Schüller, Christian
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: 530 Physik
subject: 73.20.−r, 39.30.+w, 85.75.−d, 71.70.Ej

description: We have studied the spin dynamics of a high-mobility two-dimensional electron system in a GaAs∕Al0.3Ga0.7As single quantum well by time-resolved Faraday rotation and time-resolved Kerr rotation in dependence on the initial degree of spin polarization, P, of the electrons. By increasing the initial spin polarization from the low-P regime to a significant P of several percent, we find that the spin dephasing time, T2*, increases from about 20 to 200 ps. Moreover, T2* increases with temperature at small spin polarization but decreases with temperature at large spin polarization. All these features are in good agreement with theoretical predictions by Weng and Wu [Phys. Rev. B 68, 075312 (2003)]. Measurements as a function of spin polarization at fixed electron density are performed to further confirm the theory. A fully microscopic calculation is performed by setting up and numerically solving the kinetic spin Bloch equations, including the D’yakonov-Perel’ and the Bir-Aronov-Pikus mechanisms, with all the scattering explicitly included. We reproduce all principal features of the experiments, i.e., a dramatic decrease of spin dephasing with increasing P and the temperature dependences at different spin polarizations.
A Census of Mid-Infrared Selected Active Galactic Nuclei in Massive Galaxy Clusters at 0 < z < 1.3
Creators: name: Tomczak, Adam R.
name: Tran, Kim-Vy H.
name: Saintonge, Amélie
Publisher: name: arXiv
Year: 2011
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences

description: We conduct a deep mid-infrared census of nine massive galaxy clusters at (03 sigma level, we identify 12 that host mid-infrared selected active galactic nuclei (IR-AGN). To compare the IR-AGN across our redshift range, we define two complete samples of cluster galaxies: (1) optically-selected members with rest-frame V(AB) magnitude 0.5 Mpc) and are hosted by highly morphologically disturbed members. Although our sample is limited, our results suggest that \agnfrac in massive galaxy clusters is not strongly correlated with star formation at z<1, and that IR-AGN have a more prominent role at z>1.
description: 13 pages, 8 figures, accepted to the Astrophysical Journal
Dynamics of Charged Plane Symmetric Gravitational Collapse
Creators: name: Sharif, M.
name: Siddiqa, Aisha
Publisher: name: arXiv
Year: 2010
Subjects: subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences

description: In this paper, we study dynamics of the charged plane symmetric gravitational collapse. For this purpose, we discuss non-adiabatic flow of a viscous fluid and deduce the results for adiabatic case. The Einstein and Maxwell field equations are formulated for general plane symmetric spacetime in the interior. Junction conditions between the interior and exterior regions are derived. For the non-adiabatic case, the exterior is taken as plane symmetric charged Vaidya spacetime while for the adiabatic case, it is described by plane Reissner-Nordstr$\ddot{o}$m spacetime. Using Misner and Sharp formalism, we obtain dynamical equations to investigate the effects of different forces over the rate of collapse. In non-adiabatic case, a dynamical equation is joined with transport equation of heat flux. Finally, a relation between the Weyl tensor and energy density is found.
description: 21 pages, accepted for publication Gen. Relativ. Grav
Detection of coherent acoustic oscillations in a quantum electromechanical resonator
Creators: name: Beil, Florian W.
name: Blick, Robert H.
name: Wixforth, Achim
name: Wegscheider, Werner
name: Schuh, Dieter
name: Bichler, Max
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: eigenvalues and eigenfunctions, quantum computing, nanotechnology, micromechanical devices, crystal resonators, surface acoustic waves, acousto-optical effects
subject: 530 Physik
subject: 43.35.Sx; 03.67.Lx

description: Coherent control of occupation numbers in quantum mechanical multilevel systems is widely studied driven by its application in lasers and its prospects for quantum computational elements. Here the authors present a nanoelectromechanical resonator equivalent to the coherent control of a quantum mechanical two level system. The distinct eigenmodes of a nanomechanical beam resonator represent the two levels whose amplitude mode occupation numbers are controlled by a frequency matched acoustic excitation, mediated by a pulsed surface acoustic wave. They show that similar to quantum mechanical systems it is possible to transfer occupation numbers from one mode to another by matched acoustic pulses.
Reconciling resistance : women's postnatal physical activity decision-making
Creators: name: Liva, Sarah
Publisher: name: University of British Columbia
Year: 2018

description: Background: Nearly half of women have reported reducing their physical activity below recommended levels during the postpartum period and evidence suggests these reductions are sustained beyond the postnatal year. The modestly effective interventions to increase postnatal physical activity may indicate a lack of understanding about how women make postnatal physical activity choices. Research Question: What are women’s decision-making processes about physical activity in the postnatal period? Methods: I used a qualitative grounded theory methodology to develop a core category and interrelated categories explaining women’s physical activity decision-making processes during the postpartum period. Thirty women within a year of childbirth, were recruited using flyers and social media, and interviewed after they completed 3-day diaries. I open-coded the data to identify a core category, and then selectively coded, and theoretically coded to articulate relationships between the core category and other categories using constant comparative analysis. Findings: The core category, reconciling resistance, comprised three processes: gauging, engaging, and adjusting, and explained how women resolved their main concern in making physical activity decisions to minimize discord between their physical activity desires and actual physical activity patterns. Participants experienced personal embodiment, relational, environmental and physical activity centrality resistance that they reconciled through gauging the risks and accessibility of choosing their desired activities and deciding whether they regarded the activities as essential for them postnatally. The women engaged to either push through, hold back, or hold still on pursuing their desired activities and adjusted their choices of strategies in response to their experiences of engaging. Only the women who constructed their physical activities as supporting their own and others’ needs and experienced limited personal embodiment resistance (e.g., fatigue, injury) pushed through. Most women held back or held still by redefining the types of activity that they believed could support their own and others’ needs. Implications: Providing mothers with anticipatory guidance and education about safely returning to physical activity is an important strategy for health care providers to support postnatal physical activity. Increasing knowledge about physical activity choices in the context of women’s need satisfaction could support strategies that are acceptable to women within the postpartum period.
Missing conductivity peak in a surface acoustic wave measurement at ν=2/3
Creators: name: Dini, D.
name: Dunford, R. D.
name: Stern, O.
name: Dietsche, W.
name: Mellor, C. J.
name: Klitzing, Klaus von
name: Wegscheider, Werner
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: 530 Physik
subject: 73.43.Qt, 73.21.−b, 73.50.Rb

description: Surface acoustic waves (SAWs) were used to study the spin transition of the fractional quantum Hall effect at a filling factor of 2∕3. Although very distinct and hysteretic anomalies were observed at the transition in the transport measurements, no indication was visible in the SAW data. This holds true not only for the small current regime but also for the large current regime where dynamic nuclear-spin polarization enhances the effect. We suggest that this result can be accounted for by highly conducting domain walls with thicknesses of at most 1% of the typical domain size.
Asymmetric Line Profiles in Spectra of Gaseous Metal Disks Around Single White Dwarfs
Creators: name: Hartmann, S.
name: Nagel, T.
name: Rauch, T.
name: Werner, K.
Publisher: name: arXiv
Year: 2011
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences

description: Metal-rich debris disks were discovered around several single DAZ and DBZ white dwarfs, which may stem from disruption of smaller rocky planetesimals. In some cases, the material in addition forms a gaseous disk. For SDSS J122859.93+104032.9, the double peaked infrared Ca II triplet at about 8500 angstrom exhibits a strong red/violet asymmetry. With the Tuebingen non-LTE Accretion Disk code AcDc we calculated the spectrum and vertical structure of the disk, assuming the chemical mixture of the disk's material being similar to a chondrite-like asteroid, the most prominent type in our own solar system. By modifying the code to simulate different non axis-symmetrical disk geometries, the first preliminary results are in good agreement with the observed asymmetric line profile.
description: 8 pages, 5 figures, Part of PlanetsbeyondMS/2010 proceedings (arXiv:1011.6606)
Lateral diffusion of photogenerated carriers in InGaN/GaN heterostructures observed by PL measurements
Creators: name: Vierheilig, Clemens
name: Braun, H.
name: Schwarz, Ulrich
name: Wegscheider, Werner
name: Baur, E.
name: Strauß, U.
name: Härle, Volker
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: 530 Physik
subject: 78.55.Cr; 78.67.De

description: In this paper we present a direct observation of the lateral diffusion of photogenerated carriers in InGaN/GaN quantum wells. The spatial distribution of the photoluminescence around a small exciting laser spot is analyzed by scanning in the focal plane of our confocal microscope. The results of a blue and a green emitting sample at varying excitation densities are discussed in the context of the theoretical model of the enhanced lateral diffusion. A lateral electric field which causes an additional radial drift motion was determined by analyzing the PL spectra and by solving a drift-diffusion equation for the lateral motion in the quantum well.
Generic strange duality for $K3$ surfaces
Creators: name: Marian, Alina
name: Oprea, Dragos
name: Yoshioka, Kota
Publisher: name: arXiv
Year: 2010
Subjects: subject: Algebraic Geometry (math.AG)
subject: FOS: Mathematics

description: Strange duality is shown to hold over generic $K3$ surfaces in a large number of cases. The isomorphism for elliptic $K3$ surfaces is established first via Fourier-Mukai techniques. Applications to Brill-Noether theory for sheaves on $K3$s are also obtained. The appendix written by Kota Yoshioka discusses the behavior of the moduli spaces under change of polarization, as needed in the argument.
description: Appendix is written by Kota Yoshioka
Illumination-induced changes of the Fermi surface topology in three-dimensional superlattices
Creators: name: Goncharuk, N. A.
name: Smrčka, L.
name: Svoboda, P.
name: Vašek, P.
name: Kučera, J.
name: Krupko, Yu
name: Wegscheider, Werner
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: 530 Physik
subject: 73.43.Qt, 73.43.Jn, 02.60.Ed, 03.65.Sq

description: The magnetoresistance of the molecular beam epitaxy grown GaAs∕Al0.3Ga0.7As superlattice with Si-doped barriers has been measured in tilted magnetic fields in the as-grown state and after brief illumination by a red-light diode at low temperature, T≈0.3 K. A remarkable illumination-induced modification of magnetoresistance curves has been observed, which indicates a significant change of the superlattice Fermi surface topology. Analysis of magnetoresistance data in terms of the tight-binding model reveals that not only electron concentration and mobility have been increased by illumination, but also that the coupling among two-dimensional electron layers in neighboring quantum wells has been reduced.
Influences des paramètres micromécaniques dans la simulation numérique discrète des matériaux granulaires : assemblage, déformation quasi-statique, écoulements
Creators: name: Roux, Jean-Noël
name: Chevoir, François
Publisher: name: arXiv
Year: 2010
Subjects: subject: Soft Condensed Matter (cond-mat.soft)
subject: FOS: Physical sciences

description: We review the influence of micromechanical parameters on the macroscopic mechanical behaviour of granular materials, as numerically simulated in discrete element approaches, both in quasistatic conditions an din dense flow. We insist in particular on the role of suitably defined dimensionless numbers apt to provide a classification of rheological regimes of quite general validity.
description: 27 pages
Decoherence and single electron charging in an electronic Mach-Zehnder interferometer
Creators: name: Litvin, Leonid
name: Tranitz, Hans-Peter
name: Wegscheider, Werner
name: Strunk, Christoph
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: 530 Physik
subject: 73.23.Ad, 73.63.Nm

description: We investigate the temperature and voltage dependence of the quantum interference in an electronic Mach-Zehnder interferometer using edge channels in the integer quantum-Hall regime. The amplitude of the interference fringes is significantly smaller than expected from theory; nevertheless the functional dependence of the visibility on temperature and bias voltage agrees very well with theoretical predictions. Superimposed on the Aharonov-Bohm (AB) oscillations, a conductance oscillation with a six times smaller period is observed. The latter depends only on gate voltage and not on the AB phase, and may be related to single electron charging.
Derivation of an Abelian effective model for instanton chains in 3D Yang-Mills theory
Creators: name: de Lemos, A. L. L.
name: Oxman, L. E.
name: Teixeira, B. F. I.
Publisher: name: arXiv
Year: 2011
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: High Energy Physics - Phenomenology (hep-ph)
subject: FOS: Physical sciences

description: In this work, we derive a recently proposed Abelian model to describe the interaction of correlated monopoles, center vortices, and dual fields in three dimensional SU(2) Yang-Mills theory. Following recent polymer techniques, special care is taken to obtain the end-to-end probability for a single interacting center vortex, which constitutes a key ingredient to represent the ensemble integration.
description: 18 pages, LaTeX
Two beam Aharonov–Bohm interference in the integer quantum Hall regime
Creators: name: Litvin, Leonid
name: Helzel, Andreas
name: Tranitz, Hans-Peter
name: Wegscheider, Werner
name: Strunk, Christoph
Publisher: name: Universität Regensburg
Year: 2008
Subjects: subject: Electron interference; Quantum point contact; Quantum Hall effect
subject: 530 Physik
subject: 73.23.Ad; 73.63.Nm

description: We study an electronic Mach–Zehnder interferometer employing the edge channels of a two-dimensional electron gas (2DEG) in the quantum Hall regime and quantum point contacts (QPC) as beam splitters. The linear conductance of the QPC as a function of gate voltage shows resonances superimposed on quantized conductance steps. It was found that the visibility depends strongly on magnetic field and is highest near a filling factor of 1.5 in the interferometer arm.
Discrete charging of traps visualized by scanning gate experiments on a quantum point contact
Creators: name: Pioda, A.
name: Kičin, S.
name: Brunner, D.
name: Ihn, Thomas
name: Sigrist, Martin
name: Ensslin, Klaus
name: Reinwald, Matthias
name: Wegscheider, Werner
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: 530 Physik
subject: 74.50.+r

description: A quantum point contact (QPC) patterned on a two-dimensional electron gas is investigated with a scanning gate setup operated at a temperature of 300 mK. The conductance of the point contact is recorded while the local potential is modified by scanning the tip. Discrete charging of traps induced by the local potential is observed as a stepwise conductance change of the constriction. By selectively changing the state of some of these traps, it is possible to observe changes in the transmission of the QPC. The lateral position of such traps is determined, and their density is estimated to be below 50 per μm2, corresponding to less than 1% of the doping concentration.
Efficient generation of universal two-dimensional cluster states with hybrid systems
Creators: name: Lin, Qing
name: He, Bing
Publisher: name: arXiv
Year: 2010
Subjects: subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: We present a scheme to generate two-dimensional cluster state efficiently. The number of the basic gate-entangler-for the operation is in the order of the entanglement bonds of a cluster state, and could be reduced greatly if one uses them repeatedly. The scheme is deterministic and uses few ancilla resources and no quantum memory. It is suitable for large-scale quantum computation and feasible with the current experimental technology.
description: 6 pages, 5 figures
Is inelastic cotunneling phase coherent?
Creators: name: Sigrist, Martin
name: Ihn, Thomas
name: Ensslin, Klaus
name: Reinwald, Matthias
name: Wegscheider, Werner
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: Aharonov-Bohm effect, Coulomb blockade, quantum dots, tunnelling
subject: 530 Physik
subject: 73.23.Hk; 73.63.Kv; 73.21.La

description: For low biases the linear conductance of quantum dots is based on elastic transport processes. At finite bias in the Coulomb blockade regime, inelastic cotunneling sets in once the applied bias exceeds the energy between ground and excited state in the dot. Here we report on transport experiments through an Aharonov-Bohm ring containing a quantum dot in each arm of the ring. The tunnel coupling between the two dots can be tuned by electrostatic gates. For strong tunnel coupling and low bias we observe pronounced Aharonov-Bohm oscillations in the ring with visibilities exceeding 80%. For quantum dots which are purely capacitively coupled, the Aharonov-Bohm amplitude is reduced to a more standard 10%. For finite bias, where transport through excited states becomes possible and a conductance onset is observed, the visibility of the Aharonov-Bohm oscillations remains basically unchanged, while the phase typically undergoes a change of pi. We discuss these observations in view of the possible elastic and inelastic transport processes and their contributions to coherent transport.
From geodesics of the multipole solutions to the perturbed Kepler problem
Creators: name: Hernandez-Pastora, J. L.
name: Ospino, J.
Publisher: name: arXiv
Year: 2010
Subjects: subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences

description: A static and axisymmetric solution of the Einstein vacuum equations with a finite number of Relativistic Multipole Moments (RMM) is written in MSA coordinates up to certain order of approximation, and the structure of its metric components is explicitly shown. From the equation of equatorial geodesics we obtain the Binet equation for the orbits and it allows us to determine the gravitational potential that leads to the equivalent classical orbital equations of the perturbed Kepler problem. The relativistic corrections to Keplerian motion are provided by the different contributions of the RMM of the source starting from the Monopole (Schwarzschild correction). In particular, the perihelion precession of the orbit is calculated in terms of the quadrupole and 2$^4$-pole moments. Since the MSA coordinates generalize the Schwarzschild coordinates, the result obtained allows measurement of the relevance of the quadrupole moment in the first order correction to the perihelion frequency-shift.
Start-up incubators for refugees: Applying psychological methods to increase chances of entrepreneurial success
Creators: name: Hinz, Andreas
name: Nido, Miriam
name: Hell, Benedikt
Publisher: name: Academic Conferences International Limited
Year: 2023
Subjects: subject: entrepreneurship
subject: startup incubator
subject: refugees
subject: 330 - Wirtschaft
subject: 360 - Soziale Probleme, Sozialdienste, Versicherungen

description: An increasing number of start-up incubators offer programmes designed specifically for refugees. They provide entrepreneurship training and access to a closely-knit community for start-up development. Beyond that, they also support refugees in overcoming typical challenges, including a lack of language skills and required qualifications, an uncertain residence status, discrimination and psychological distress on various levels. While these incubators have already contributed to refugees’ social and economic integration, the number of successful participants is still relatively low. The question remains about what can be done to multiply the potential so that more significant numbers of refugees can benefit. To support incubators in achieving more significant numbers, this work presents a framework of methods and tools based on health and organisational psychology literature. More specifically, this work focuses on methods and tools to be applied during two critical phases of the incubation cycle, namely the selection process and the actual programme.
Anomalous Enhancement of the Superconducting Transition Temperature in Electron-Doped Cuprate Heterostructures
Creators: name: Jin, K.
name: Bach, P.
name: Zhang, X. H.
name: Grupel, U.
name: Zohar, E.
name: Diamant, I.
name: Dagan, Y.
name: Smadici, S.
name: Abbamonte, P.
name: Greene, R. L.
Publisher: name: arXiv
Year: 2011
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: The superconducting transition temperature $T_{c}$ of multilayers of electron-doped cuprates, composed of underdoped (or undoped) and overdoped La% $_{2-x}$Ce$_{x}$CuO$_{4}$ (LCCO) and Pr$_{2-x}$Ce$_{x}$CuO$_{4}$ (PCCO) thin films, is found to increase significantly with respect to the $T_{c}$ of the corresponding single-phase films. By investigating the critical current density of superlattices with different doping levels and layer thicknesses, we find that the $T_{c}$ enhancement is caused by a redistribution of charge over an anomalously large distance.
description: 4 figures. To appear in PRB as a Rapid Communication
Rashba and Dresselhaus spin splittings in semiconductor quantum wells measured by spin photocurrents
Creators: name: Giglberger, Stephan
name: Golub, Leonid E.
name: Belkov, Vassilij
name: Danilov, Sergey
name: Schuh, Dieter
name: Gerl, Christian
name: Rohlfing, Franziska
name: Stahl, Joachim
name: Wegscheider, Werner
name: Weiss, Dieter
name: Prettl, Wilhelm
name: Ganichev, Sergey
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: 530 Physik
subject: 73.21.Fg, 72.25.Fe, 78.67.De, 73.63.Hs

description: The spin-galvanic effect and the circular photogalvanic effect induced by terahertz radiation are applied to determine the relative strengths of Rashba and Dresselhaus band spin splitting in (001)-grown GaAs and InAs based two dimensional electron systems. We observed that shifting the δ-doping plane from one side of the quantum well to the other results in a change of sign of the photocurrent caused by Rashba spin splitting while the sign of the Dresselhaus term induced photocurrent remains. The measurements give the necessary feedback for technologists looking for structures with equal Rashba and Dresselhaus spin splittings or perfectly symmetric structures with zero Rashba constant.
Strong Electron Confinement By Stacking-fault Induced Fractional Steps on Ag(111) Surfaces
Creators: name: Uchihashi, Takashi
name: Kobayashi, Katsuyoshi
name: Nakayama, Tomonobu
Publisher: name: arXiv
Year: 2010
Subjects: subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: FOS: Physical sciences

description: The electron reflection amplitude $R$ at stacking-fault (SF) induced fractional steps is determined for Ag(111) surface states using a low temperature scanning tunneling microscope. Unexpectedly, $R$ remains as high as $0.6 \sim 0.8$ as energy increases from 0 to 0.5 eV, which is in clear contrast to its rapidly decreasing behavior for monatomic (MA) steps [L. B{ü}rgi et al., Phys. Rev. Lett. \textbf{81}, 5370 (1998)]. Tight-binding calculations based on {\em ab-initio} derived band structures confirm the experimental finding. Furthermore, the phase shifts at descending SF steps are found to be systematically larger than counterparts for ascending steps by $\approx 0.4 π$. These results indicate that the subsurface SF plane significantly contributes to the reflection of surface states.
Superhumps and their Amplitudes
Creators: name: Smak, J.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences

description: Superhump amplitudes observed in dwarf novae during their superoutbursts depend on orbital inclination: the maximum amplitudes in systems with low inclinations are $A_\circ \approx 0.25$ mag., while at higher inclinations they increase from $A_\circ \sim 0.3$ to $A_\circ \sim 0.6$ mag. The mean maximum superhump amplitudes normalized to the average luminosity of the disk are: $=0.34\pm 0.02$ in low inclination systems and only $=0.17\pm 0.01$ in high inclination systems. This shows that at high inclinations the superhump lIght source is {\it partly} obscured by the disk edge and implies that it is located close to the disk surface but extends sufficiently high above that surface to avoid full obscuration. Superhump amplitudes in high inclination systems show modulation with beat phase ($ϕ_b$), interpreted as being due to azimuth-dependent obscuration effects in a non-axisymmetric disk. In addition they show modulation with $2ϕ_b$ which implies that the orientation of the superhump light source is correlated with the direction of the stream. The dependence of superhump amplitudes on orbital inclination and their modulation with beat phase eliminate the tidal-resonance model for superhumps. Instead they support an alternative interpretation of superhumps as being due to periodically modulated dissipation of the kinetic energy of the stream. Superhump amplitudes in permanent superhumpers are $=0.12$, i.e. much smaller than the maximum amplitudes observed during superoutbursts.
description: 16 pages, 5 figures, 3 tables. Submitted to "Acta Astronomica"
The Rap GTPases coordinate actin and microtubule cytoskeleton reorganization, and promote antigen extraction at the B cell immune synapse
Creators: name: Wang, Jia Chao
Publisher: name: University of British Columbia
Year: 2019

description: B cells that bind antigens displayed on antigen-presenting cells (APCs) form an immune synapse (IS), a polarized cellular structure that optimizes the dual functions of the B cell receptor (BCR), signal transduction and antigen internalization. Immune synapse formation involves the polarization of the microtubule-organizing center (MTOC) towards the APC. I showed that BCR-induced MTOC polarization requires the Rap1 GTPases (which has two isoforms, Rap1a and Rap1b), an evolutionarily conserved regulator of cell polarity, as well as cofilin-1, an actin-severing protein that is regulated by Rap1. MTOC reorientation towards the antigen contact site correlated strongly with cofilin-1-dependent actin reorganization and cell spreading. I also showed that BCR-induced MTOC polarization requires the dynein motor protein as well as IQGAP1, a scaffolding protein that can link the actin and microtubule cytoskeletons. At the periphery of the immune synapse, IQGAP1 associates closely with F-actin structures and with the microtubule plus-end-binding protein CLIP-170. Moreover, the accumulation of IQGAP1 at the antigen contact site depends on F-actin reorganization that is controlled by Rap1 and cofilin-1. I also demonstrate that the hematopoietic-cell specific cortactin-homologue, HS1, is essential for regulating actin cytoskeletal remodeling during immune synapse formation and acts downstream of Rap to promote BCR-induced antigen gathering. Additionally, inhibiting the Rap1-cofilin-1 pathway, CLIP-170 expression, or cytoskeletal dynamics impairs the ability of B cells to acquire antigens from APCs. Thus, Rap1 coordinates actin and microtubule organization at the IS, facilitating antigen acquisition from APCs.
Effect of Initial Spin Polarization on Spin Dephasing and the Electron g Factor in a High-Mobility Two-Dimensional Electron System
Creators: name: Stich, Dominik
name: Zhou, J.
name: Korn, Tobias
name: Schulz, Robert
name: Schuh, Dieter
name: Wegscheider, Werner
name: Wu, Meng W.
name: Schüller, Christian
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: 530 Physik
subject: 71.70.Ej, 39.30.+w, 73.20.−r, 85.75.−d

description: We have investigated the spin dynamics of a high-mobility two-dimensional electron system (2DES) in a GaAs-Al0.3Ga0.7As single quantum well by time-resolved Faraday rotation in dependence on the initial degree of spin polarization, P, of the 2DES. From P∼0 to P∼30%, we observe an increase of the spin dephasing time, T2*, by an order of magnitude, from about 20 ps to 200 ps, in good agreement with theoretical predictions by Weng and Wu [Phys. Rev. B 68, 075312 (2003)]. Furthermore, also the electron g factor is found to decrease for increasing P. Fully microscopic calculations reproduce the most salient features of the experiments, i.e., a dramatic decrease of spin dephasing and a moderate decrease of the electron g factor with increasing P. We show that both results are determined dominantly by the Hartree-Fock contribution of the Coulomb interaction.