cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
The Mechanical Greenhouse: Burial of Heat by Turbulence in Hot Jupiter Atmospheres
Creators: name: Youdin, Andrew N.
name: Mitchell, Jonathan L.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences

description: The intense irradiation received by hot Jupiters suppresses convection in the outer layers of their atmospheres and lowers their cooling rates. "Inflated" hot Jupiters, i.e., those with anomalously large transit radii, require additional sources of heat or suppressed cooling. We consider the effect of forced turbulent mixing in the radiative layer, which could be driven by atmospheric circulation or by another mechanism. Due to stable stratification in the atmosphere, forced turbulence drives a downward flux of heat. Weak turbulent mixing slows the cooling rate by this process, as if the planet was irradiated more intensely. Stronger turbulent mixing buries heat into the convective interior, provided the turbulence extends to the radiative-convective boundary. This inflates the planet until a balance is reached between the heat buried into and radiated from the interior. We also include the direct injection of heat due to the dissipation of turbulence or other effects. Such heating is already known to slow planetary cooling. We find that dissipation also enhances heat burial from mixing by lowering the threshold for turbulent mixing to drive heat into the interior. Strong turbulent mixing of heavy molecular species such as TiO may be necessary to explain stratospheric thermal inversions. We show that the amount of mixing required to loft TiO may overinflate the planet by our mechanism. This possible refutation of the TiO hypothesis deserves further study. Our inflation mechanism requires a deep stratified layer that only exists when the absorbed stellar flux greatly exceeds the intrinsic emitted flux. Thus it would be less effective for more luminous brown dwarfs and for longer period gas giants, including Jupiter and Saturn.
description: 15 pages, 8 figures, accepted for publication in ApJ
How Do We Diversify Human Genomics Research?
Creators: name: Popejoy, Alice
Publisher: name: Center for ELSI Resources and Analysis
Year: 2023
Subjects: subject: Genetics
subject: FOS: Biological sciences
subject: Ethics
subject: Science
subject: ELSI
subject: genetic diversity
subject: admixture
subject: anti-racism
subject: FAIR data principles

description: The lack of diversity in human genomics research and reference datasets is a known problem, with real-life consequences, but the path forward remains elusive. Solutions to the problem of sampling bias in human genetics research must begin by understanding the following: 1) historical influences and current problems with classification, study design, and conceptual frameworks in human genetics research; 2) tensions between characterizing who has been included in (and excluded from) research, and biases that are introduced through categorizing humans by social and cultural population descriptors (e.g., race, ethnicity, ancestry); and 3) how a lack of diversity and conceptual clarity in human genomics leads to disparities in clinical genetics and precision medicine. Finally, we must recognize how a lack of diversity in the genomics workforce perpetuates these blind spots and how active recruitment and promotion of people from all backgrounds improves both our science and workplace environments.
Analytic Calculation of Neutrino Mass Eigenvalues
Creators: name: Chaturvedi, K.
name: Koranga, Bipin Singh
name: Kumar, Vinod
Publisher: name: arXiv
Year: 2011
Subjects: subject: High Energy Physics - Phenomenology (hep-ph)
subject: FOS: Physical sciences

description: Implicaion of the neutrino oscillation search for the neutrino mass square difference and mixing are discussed. We have considered the effective majorana mass m_{ee}, related for ββ_{0ν}decay. We find limits for neutrino mass eigen value m_{i} in the different neutrino mass spectrum,which explain the different neutrino data.
description: 10 pages
On the Baltimore Light RailLink into the quantum future
Creators: name: Domino, Krzysztof
name: Doucet, Emery
name: Robertson, Reece
name: Gardas, Bart?Omiej
name: Deffner, Sebastian
Publisher: name: Maryland Shared Open Access Repository
Year: 2024
Subjects: subject: Quantum Physics
subject: FOS: Physical sciences
subject: UMBC Quantum Thermodynamics Group

description: In the current era of noisy intermediate-scale quantum (NISQ) technology, quantum devices present new avenues for addressing complex, real-world challenges including potentially NP-hard optimization problems. This work aims to showcase how the inherent noise in NISQ devices can be leveraged to solve such real-world problems effectively. Utilizing a D-Wave quantum annealer and IonQ's gate-based NISQ computers, we generate and analyze solutions for managing train traffic under stochastic disturbances. Our case study focuses on the Baltimore Light RailLink, which embodies the characteristics of both tramway and railway networks. We explore the feasibility of using NISQ technology to model the stochastic nature of disruptions in these transportation systems. Our research marks the inaugural application of both quantum computing paradigms to tramway and railway rescheduling, highlighting the potential of quantum noise as a beneficial resource in complex optimization scenarios.
The Pulsar Search Collaboratory
Creators: name: Rosen, Rachel
name: Heatherly, Sue Ann
name: McLaughlin, Maura A.
name: Lynch, Ryan
name: Kondratiev, Vlad I.
name: Boyles, Jason R.
name: Wilson, M. Terry
name: Lorimer, Duncan R.
name: Ransom, Scott
Publisher: name: arXiv
Year: 2010
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: FOS: Physical sciences

description: The Pulsar Search Collaboratory [PSC, NSF #0737641] is a joint project between the National Radio Astronomy Observatory (NRAO) and West Virginia University (WVU) designed to interest high school students in science, technology, engineering, and mathematics [STEM] related career paths by helping them to conduct authentic scientific research. The 3- year PSC program, which began in summer 2008, teaches students to analyze astronomical radio data acquired with the 100-m Robert C. Byrd Green Bank Telescope for the purpose of discovering new pulsars. We present the results of the first complete year of the PSC, which includes two astronomical discoveries.
description: 18 pages, 7 figures
Parsec-Scale Bipolar X-ray Shocks Produced by Powerful Jets from the Neutron Star Circinus X-1
Creators: name: Sell, P. H.
name: Heinz, S.
name: Calvelo, D. E.
name: Tudose, V.
name: Soleri, P.
name: Fender, R. P.
name: Jonker, P. G.
name: Schulz, N. S.
name: Brandt, W. N.
name: Nowak, M. A.
name: Wijnands, R.
name: van der Klis, M.
name: Casella, P.
Publisher: name: arXiv
Year: 2010
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences

description: We report the discovery of multi-scale X-ray jets from the accreting neutron star X-ray binary, Circinus X-1. The bipolar outflows show wide opening angles and are spatially coincident with the radio jets seen in new high-resolution radio images of the region. The morphology of the emission regions suggests that the jets from Circinus X-1 are running into a terminal shock with the interstellar medium, as is seen in powerful radio galaxies. This and other observations indicate that the jets have a wide opening angle, suggesting that the jets are either not very well collimated or precessing. We interpret the spectra from the shocks as cooled synchrotron emission and derive a cooling age of approximately 1600 yr. This allows us to constrain the jet power to be between 3e35 erg/s and 2e37 erg/s, making this one of a few microquasars with a direct measurement of its jet power and the only known microquasar that exhibits stationary large-scale X-ray emission.
description: 5 pages, 4 figures, to be published in the Astrophysical Journal Letters
A New Combined European Permanent Network Station Coordinates Solution
Creators: name: Panafidina, N.
name: Malkin, Z.
name: Weber, R.
Publisher: name: arXiv
Year: 2011
Subjects: subject: Geophysics (physics.geo-ph)
subject: FOS: Physical sciences

description: The EUREF (International Association of Geodesy (IAG) Reference Frame Sub-Commission for Europe) network of continuously operating GPS stations (EPN) was primarily established for reference frame maintenance, and also plays an important role for geodynamical research in Europe. The main goal of this paper is to obtain an independent homogeneous time-series of the EPN station coordinates, which is also available in SINEX format. A new combined solution of the EPN station coordinates was computed. The combination was performed independently for every week, in three steps: 1. the stated constraints on the coordinates were removed from the individual solutions of the Analysis Centers; 2. the de-constrained solutions were aligned to ITRF2000; 3. the resulting solutions were combined using the Helmert block-ing technique. All the data from GPS week 900 to week 1302 (April 1997 - December 2004) were used. We investigated in detail the behavior of the transformation parameters aligning the new combined solution to ITRF2000. In general, the time-series of the transformation parameters show a good stability in time although small systematic effects can be seen, most likely caused by station instabilities. A comparison of the new combined solution to the official EUREF weekly combined solution is also presented.
Reversal of Nonlocal Vortex Motion in the Regime of Strong Nonequilibrium
Creators: name: Otto, Florian
name: Bilusic, Ante
name: Babic, Dinko
name: Vodolazov, D. Yu
name: Sürgers, Christoph
name: Strunk, Christoph
Publisher: name: Universität Regensburg
Year: 2010
Subjects: subject: 530 Physik
subject: 74.25.Uv
subject: 74.25.F-
subject: 74.78.Na

description: We investigate nonlocal vortex motion in weakly pinning a-NbGe nanostructures, which is driven by a transport current I and remotely detected as a nonlocal voltage Vnl. At a high I of a given polarity, Vnl changes sign dramatically. This is followed by Vnl becoming even in I, with the opposite sign at low and high temperatures T. These findings can be explained by a Nernst-like effect resulting from local electron overheating (low T), and a magnetization enhancement due to a nonequilibrium quasiparticle distribution that leads to a gap enhancement near the vortex core (high T).
Hybrid quantum-classical computation for automatic guided vehicles scheduling
Creators: name: ?Mierzchalski, Tomasz
name: Paw?Owski, Jakub
name: Przybysz, Artur
name: Pawela, ?Ukasz
name: Pucha?A, Zbigniew
name: Koniorczyk, Mátyás
name: Gardas, Bart?Omiej
name: Deffner, Sebastian
name: Domino, Krzysztof
Publisher: name: Maryland Shared Open Access Repository
Year: 2024
Subjects: subject: Quantum Physics
subject: FOS: Physical sciences
subject: UMBC Quantum Thermodynamics Group
subject: Computer Science - Emerging Technologies

description: Motivated by recent efforts to develop quantum computing for practical, industrial-scale challenges, we demonstrate the effectiveness of state-of-the-art hybrid (not necessarily quantum) solvers in addressing the business-centric optimization problem of scheduling Automatic Guided Vehicles (AGVs). Some solvers can already leverage noisy intermediate-scale quantum (NISQ) devices. In our study, we utilize D-Wave hybrid solvers that implement classical heuristics with potential assistance from a quantum processing unit. This hybrid methodology performs comparably to existing classical solvers. However, due to the proprietary nature of the software, the precise contribution of quantum computation remains unclear. Our analysis focuses on a practical, business-oriented scenario: scheduling AGVs within a factory constrained by limited space, simulating a realistic production setting. Our approach maps a realistic AGVs problem onto one reminiscent of railway scheduling and demonstrates that the AGVs problem is better suited to quantum computing than its railway counterpart, the latter being denser in terms of the average number of constraints per variable. The main idea here is to highlight the potential usefulness of a hybrid approach for handling AGVs scheduling problems of practical sizes. We show that a scenario involving up to 21 AGVs, significant due to possible deadlocks, can be efficiently addressed by a hybrid solver in seconds.
Time-Changed Poisson Processes
Creators: name: Kumar, A.
name: Nane, Erkan
name: Vellaisamy, P.
Publisher: name: arXiv
Year: 2011
Subjects: subject: Probability (math.PR)
subject: Mathematical Physics (math-ph)
subject: FOS: Mathematics
subject: FOS: Physical sciences

description: We consider time-changed Poisson processes, and derive the governing difference-differential equations (DDE) these processes. In particular, we consider the time-changed Poisson processes where the the time-change is inverse Gaussian, or its hitting time process, and discuss the governing DDE's. The stable subordinator, inverse stable subordinator and their iterated versions are also considered as time-changes. DDE's corresponding to probability mass functions of these time-changed processes are obtained. Finally, we obtain a new governing partial differential equation for the tempered stable subordinator of index $0
description: 18 pages
Place and culture in identity construction and negotiation : the case of Hong Kong
Creators: name: Me, Carmut
Publisher: name: University of British Columbia
Year: 2018

description: Identity, a contested subject in postcolonial and global cities, is discussed in this thesis as a construct that is represented in the processes of cultural production and consumption of “places”. The postcolonial global city is where identities and cultures blend and contradict, and also where new identities and cultures arise. Portrayed as a space of “in-between” - not entirely “Western” nor exclusively Chinese, Hong Kong demonstrates the complexities of multiple global cultural flows mixing with local and national aspirations of identity. Exactly at a time when the new government and citizens are grasping the identity and culture that is unique to Hong Kong, it threatens to “disappear” in a political and cultural sense (Abbas, 1997). The struggles to define Hong Kong’s identity are exemplified in the outcomes and negotiations of the city’s spatial processes – urban development, renewal, and heritage preservation. Two cases in the cultural production of space are investigated. As studies in contrast: the grand development of the to-be international arts destination West Kowloon Cultural District that symbolizes Hong Kong’s global aspiration, and the local residents’ struggle for the preservation of Wing Lee Street representing the values of Hong Kong’s working class. The narratives of identity projected by those in power (elites, states, markets) are found to contradict with how Hong Kong people identify themselves and their city, and these contradictions are demonstrated in the place negotiations in the city.
Supplemental Information from A Morrison stem gekkotan reveals gecko evolution and Jurassic biogeography
Creators: name: Meyer, Dalton
name: Brownstein, Chase D.
name: Jenkins, Kelsey M.
name: Gauthier, Jacques A.
Publisher: name: The Royal Society
Year: 2023
Subjects: classificationCode: 310401
subject: Animal systematics and taxonomy
classificationCode: 310411
subject: Plant and fungus systematics and taxonomy
classificationCode: 310499
subject: Evolutionary biology not elsewhere classified
classificationCode: 370506
subject: Palaeontology (incl. palynology)

description: Document with expanded morphological description and phylogenetic results as well as a definintion of Ardeosauridae.
Nonlinearity from quantum mechanics: Dynamically unstable Bose-Einstein condensate in a double-well trap
Creators: name: Javanainen, Juha
Publisher: name: arXiv
Year: 2010
Subjects: subject: Quantum Physics (quant-ph)
subject: Quantum Gases (cond-mat.quant-gas)
subject: FOS: Physical sciences

description: We study theoretically an atomic Bose-Einstein condensate in a double-well trap both quantum mechanically and classically under conditions such that in the classical model an unstable equilibrium dissolves into large-scale oscillations of the atoms between the potential wells. Quantum mechanics alone does not exhibit such nonlinear dynamics, but measurements of the atom numbers in the potential wells may nevertheless cause the condensate to behave essentially classically.
description: very close to published version
The Solar Neighborhood. XXII. Parallax Results from the CTIOPI 0.9m Program: Trigonometric Parallaxes of 64 Nearby Systems with 0\farcs5 $\leq μ\leq$ 1\farcs0 yr$^{-1}$ (SLOWMO sample)
Creators: name: Riedel, Adric R.
name: Subasavage, John P.
name: Finch, Charlie T.
name: Jao, Wei Chun
name: Henry, Todd J.
name: Winters, Jennifer G.
name: Brown, Misty A.
name: Ianna, Philip A.
name: Costa, Edgardo
name: Mendez, Rene A.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences

description: We present trigonometric parallaxes of 64 stellar systems with proper motions between 0\farcs5 yr$^{-1}$ and 1\farcs0 yr$^{-1}$ from the ongoing RECONS (Research Consortium On Nearby Stars) parallax program at CTIO (the Cerro Tololo Interamerican Observatory). All of the systems are south of DEC $= +30$, and 58 had no previous trigonometric parallaxes. In addition to parallaxes for the systems, we present proper motions, Johnson-Kron-Cousins $VRI$ photometry, variability measurements, and spectral types. Nine of the systems are multiple; we present results for their components, three of which are new astrometric detections. Of the 64 systems, 56 are within 25 parsecs of the Sun and 52 of those are in the southern hemisphere, comprising 5.7\% of the total number of known southern 25 parsec systems.
description: Figures not inline. Accepted by AJ
Ferromagnet-semiconductor hybrid structures: Hall devices and tunnel junctions
Creators: name: Kreuzer, Stephan
name: Rahm, Michael
name: Biberger, Josef
name: Pulwey, Ralph
name: Raabe, Jörg
name: Schuh, Dieter
name: Wegscheider, Werner
name: Weiss, Dieter
Publisher: name: Universität Regensburg
Year: 2003
Subjects: subject: Micro-Hall magnetometry; Nanomagnets; Magnetic tunneling; Spin injection
subject: 530 Physik
subject: 73.50.Jt; 75.75.+a; 73.40.Gk; 72.25.−b

description: For spintronics, both, the properties of small ferromagnetic particles as well as the properties of ferromagnet-semiconductor hybrid structures are of importance. Below we describe how micro-Hall magnetometry provides information about the magnetisation switching of small ferromagnetic particles. In the second part we demonstrate spin dependent transport through thin GaAs membranes. The latter experiments point to the important role of spin-flip scattering in ferromagnet-semiconductor hybrid structures.
Anti-proximity Effect in Aluminum Nanowires
Creators: name: Singh, Meenakshi
name: Wang, Jian
name: Tian, Mingliang
name: Mallouk, T. E.
name: Chan, Moses H. W.
Publisher: name: arXiv
Year: 2011
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: FOS: Physical sciences

description: The anti-proximity effect, where the superconductivity in superconducting nanowires is suppressed or weakened when contacted by bulk superconducting electrodes, first revealed in arrays of Zn nanowires by tuning the electrodes from the superconducting to the normal state by means of an external magnetic field, has been confirmed in single crystal Aluminum nanowires. The critical current at zero magnetic field of an individual aluminum nanowire contacted by superconducting electrodes was found to be significantly smaller than that with normal electrodes showing that the effect is not a consequence of the magnetic field.
Fundamental changes in the composition of escaping ions at Mars induced by the December 2023 space weather event
Creators: name: Hanley, Kathleen Gwen
name: Mitchell, David
name: Lillis, Robert James
name: Fowler, Christopher M.
name: Mcfadden, James P.
name: Jolitz, Rebecca Dawn
name: Xu, Shaosui
name: Benna, Mehdi
name: Espley, Jared Randolph
name: Eparvier, Francis G.
name: Curry, Shannon M.
Publisher: name: Maryland Shared Open Access Repository
Year: 2024

description: Mars’ dayside ionosphere is maintained primarily by ionization from solar ultraviolet photons and subsequent chemical reactions, with small contributions from other mechanisms such as impact ionization and charge exchange. In December 2023, the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observed the impact of an interplanetary coronal mass ejection (ICME) on Mars’ ionosphere, including strongly enhanced ?uxes of suprathermal electrons. We show that this enhancement in suprathermal electron ?uxes increased ion production from electron impact, so that dayside electron impact ionization rates exceeded photoionization rates during the ICME. This change in ion production mechanisms led to unusually high densities of the minor ions C+ and O++. Space weather events are known to increase ion escape rates, so changes in ion composition during space weather events have important implications for atmospheric evolution. We show that scaling nominal loss rates to account for space weather may underestimate carbon loss from Mars’ atmosphere.
Fractional quantum Hall effects in bilayers in the presence of inter-layer tunneling and charge imbalance
Creators: name: Peterson, Michael R.
name: Papic, Z.
name: Sarma, S. Das
Publisher: name: arXiv
Year: 2010
Subjects: subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: FOS: Physical sciences

description: Two-component fractional quantum Hall systems are providing a major motivation for a large section of the physics community. Here we study two-component fractional quantum Hall systems in the spin-polarized half-filled lowest Landau level (filling factor 1/2) and second Landau level (filling factor 5/2) with exact diagonalization utilizing both the spherical and torus geometries. The two distinct two-component systems we consider are the true bilayer and effective bilayers (wide-quantum-well). In each model (bilayer and wide-quantum-well) we completely take into account inter-layer tunneling and charge imbalancing terms. We find that in the half-filled lowest Landau level, the FQHE is described by the two-component Abelian Halperin 331 state which is remarkably robust to charge imbalancing. In the half-filled second Landau, we find that the FQHE is likely described by the non-Abelian Moore-Read Pfaffian state which is also quite robust to charge imbalancing. Furthermore, we suggest the possibility of experimentally tuning from an Abelian to non-Abelian FQHE state in the second Landau level, and comment on recent experimental studies of FQHE in wide quantum well structures.
description: 25 pages, 27 figures
Fabrication of single crystal GaAs(001) barriers for magnetic tunnel junctions
Creators: name: Kreuzer, Stephan
name: Wegscheider, Werner
name: Weiss, Dieter
Publisher: name: Universität Regensburg
Year: 2001
Subjects: subject: III-V semiconductors, gallium arsenide, semiconductor growth, magnetic multilayers, tunnelling, etching, semiconductor superlattices, molecular beam epitaxial growth
subject: 530 Physik
subject: 81.05.Ea; 75.70.Cn; 85.75.Dd; 81.65.Cf; 68.65.Cd; 81.15.Hi

description: A preparation method for magnetic tunnel junctions with single crystal GaAs(001) barriers is demonstrated. The method is based on an epoxy bond and stop etch technique and does not require epitaxial growth of a semiconductor on top of a metal. Stable GaAs tunnel barriers down to 6 nm in thickness were prepared. The I–V measurements show a pronounced nonlinearity. Their variation with temperature depends strongly on the barrier thickness which is weak for the 6 nm barriers, a clear indication for quantum mechanical tunneling as the dominant transport channel.
Competing quantum effects in the dynamics of a flexible water model
Creators: name: Habershon, Scott
name: Markland, Thomas E.
name: Manolopoulos, David E.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Soft Condensed Matter (cond-mat.soft)
subject: FOS: Physical sciences

description: Numerous studies have identified large quantum mechanical effects in the dynamics of liquid water. In this paper, we suggest that these effects may have been overestimated due to the use of rigid water models and flexible models in which the intramolecular interactions were described using simple harmonic functions. To demonstrate this, we introduce a new simple point charge model for liquid water, q-TIP4P/F, in which the O--H stretches are described by Morse-type functions. We have parameterized this model to give the correct liquid structure, diffusion coefficient, and infra-red absorption frequencies in quantum (path integral-based) simulations. By comparing classical and quantum simulations of the liquid, we find that quantum mechanical fluctuations increase the rates of translational diffusion and orientational relaxation in our model by a factor of around 1.15. This effect is much smaller than that observed in all previous simulations of simple empirical water models, which have found a quantum effect of at least 1.4 regardless of the quantum simulation method or the water model employed. The small quantum effect in our model is a result of two competing phenomena. Intermolecular zero point energy and tunneling effects destabilize the hydrogen bonding network, leading to a less viscous liquid with a larger diffusion coefficient. However this is offset by intramolecular zero point motion, which changes the average water monomer geometry resulting in a larger dipole moment, stronger intermolecular interactions, and slower diffusion. We end by suggesting, on the basis of simulations of other potential energy models, that the small quantum effect we find in the diffusion coefficient is associated with the ability of our model to produce a single broad O-H stretching band in the infra-red absorption spectrum.
description: Published in JCP
Scalable sequential Monte Carlo methods and probabilistic approach to combinatorial problems
Creators: name: Jun, Seong-Hwan
Publisher: name: University of British Columbia
Year: 2018

description: In this thesis, we consider two combinatorial problems arising in phylogenetics and computational forestry. We develop sequential Monte Carlo based inference methods to tackle the challenges arising from these applications. In the phylogenetics application, the SMC is placed under stringent restrictions in terms of computer memory to the point where using sufficient number of particles may be prohibitive. To that end, a new method, streaming particle filter (SPF), is proposed which alleviates this problem and study some of the theoretical properties of the algorithm, including L² convergence of the estimators derived from the SPF simulation. In the case of the computational forestry, the combinatorial problem that is tackled in this thesis is referred to as the knot matching problem. This problem is formulated as a graph matching problem on a K-partite hypergraph. A model for graph matching that admits efficient parameter inference is proposed along with a sequential Monte Carlo sampler for graph matching based on this model. A detailed background on each of the two problems are presented and evaluated on simulated and real data.
Magnetization configurations and hysteresis loops of small permalloy ellipses
Creators: name: Schneider, M.
name: Liszkowski, J.
name: Rahm, M.
name: Wegscheider, Werner
name: Weiss, Dieter
name: Hoffmann, H.
name: Zweck, J.
Publisher: name: Universität Regensburg
Year: 2003
Subjects: subject: 530 Physik

description: We investigated systematically the easy axis magnetization reversal of 20 nm thick permalloy ellipses with a fixed major axis of 1.47μm and minor axes of 0.22–1.47μm. Lorentz transmission electron microscopy was used to image the micromagnetic configurations during magnetization reversal. Hysteresis loops of single ellipses were recorded by means of micro-Hall magnetometry and could be traced back to certain reversal mechanisms observed by Lorentz microscopy. In most cases, the magnetization reversal is initiated by the evolution of a magnetization buckling, followed by the formation of a single, a double, or a trapped vortex configuration. For ellipses with high aspect ratio (length-to-width ratio), the magnetization switches in the reversed magnetic field without creation of a stable vortex configuration. Our experiments show that the characteristic field values for vortex creation, single vortex annihilation, and switching strongly depend on the shape anisotropy of the elements.
Optical Probing of a Fractionally Charged Quasihole in an Incompressible Liquid
Creators: name: Schüller, Christian
name: Broocks, Kay-Birger
name: Schröter, Patrick
name: Heyn, Christian
name: Heitmann, Detlef
name: Bichler, Max
name: Wegscheider, Werner
name: Chakraborty, Tapash
name: Apalkov, V. M.
Publisher: name: Universität Regensburg
Year: 2003
Subjects: subject: two-dimensional electron gas, photoluminescence, excitons, electric charge, quasiparticles, magnetic field effects, localised states, energy gap
subject: 530 Physik
subject: 71.30.+h, 73.43.Lp, 73.63.Kv

description: In photoluminescence spectroscopy of a low-mobility two-dimensional electron gas subjected to a quantizing magnetic field, we observe an anomaly around nu= (1/3) at a very low temperature (0.1 K) and an intermediate electron density (0.9×1011 cm–2). The anomaly is explained as due to perturbation of the incompressible liquid at the Laughlin state due to close proximity of a localized charged exciton which creates a fractionally charged quasihole in the liquid. The anomaly of ~2 meV can be destroyed by applying a small thermal energy of ~0.2 meV that is enough to close the quasihole energy gap.
Effective Mechanism for Social Recommendation of News
Creators: name: Wei, Dong
name: Zhou, Tao
name: Cimini, Giulio
name: Wu, Pei
name: Liu, Weiping
name: Zhang, Yi-Cheng
Publisher: name: arXiv
Year: 2011
Subjects: subject: Physics and Society (physics.soc-ph)
subject: Social and Information Networks (cs.SI)
subject: FOS: Physical sciences
subject: FOS: Computer and information sciences

description: Recommendation systems represent an important tool for news distribution on the Internet. In this work we modify a recently proposed social recommendation model in order to deal with no explicit ratings of users on news. The model consists of a network of users which continually adapts in order to achieve an efficient news traffic. To optimize network's topology we propose different stochastic algorithms that are scalable with respect to the network's size. Agent-based simulations reveal the features and the performance of these algorithms. To overcome the resultant drawbacks of each method we introduce two improved algorithms and show that they can optimize network's topology almost as fast and effectively as other not-scalable methods that make use of much more information.
A Hubble Space Telescope Study of Lyman Limit Systems: Census and Evolution
Creators: name: Ribaudo, Joseph
name: Lehner, Nicolas
name: Howk, J. Christopher
Publisher: name: arXiv
Year: 2011
Subjects: subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: FOS: Physical sciences

description: We present a survey for optically thick Lyman limit absorbers at z<2.6 using archival Hubble Space Telescope observations with the Faint Object Spectrograph and Space Telescope Imaging Spectrograph. We identify 206 Lyman limit systems (LLSs) increasing the number of catalogued LLSs at z<2.6 by a factor of ~10. We compile a statistical sample of 50 tau_LLS > 2 LLSs drawn from 249 QSO sight lines that avoid known targeting biases. The incidence of such LLSs per unit redshift, l(z)=dn/dz, at these redshifts is well described by a single power law, l(z) = C1 (1+z)^gamma, with gamma=1.33 +/- 0.61 at z<2.6, or with gamma=1.83 +/- 0.21 over the redshift range 0.2 < z < 4.9. The incidence of LLSs per absorption distance, l(X), decreases by a factor of ~1.5 over the ~0.6 Gyr from z=4.9 to 3.5; l(X) evolves much more slowly at low redshifts, decreasing by a similar factor over the ~8 Gyr from z=2.6 to 0.25. We show that the column density distribution function, f(N(HI)), at low redshift is not well fitted by a single power law index (f(N(HI)) = C2 N(HI)^(-beta)) over the column density range 13 < log N(HI) < 22 or log N(HI) >17.2. While low and high redshift f(N(HI)) distributions are consistent for log N(HI)>19.0, there is some evidence that f(N(HI)) evolves with z for log N(HI) < 17.7, possibly due to the evolution of the UV background and galactic feedback. Assuming LLSs are associated with individual galaxies, we show that the physical cross section of the optically thick envelopes of galaxies decreased by a factor of ~9 from z~5 to 2 and has remained relatively constant since that time. We argue that a significant fraction of the observed population of LLSs arises in the circumgalactic gas of sub-L* galaxies.
description: Accepted by ApJ
Effects of bicarbonate on cardiac function in fish
Creators: name: Lo, Wing Man Mandy
Publisher: name: University of British Columbia
Year: 2018

description: An entirely novel mechanism to modulate heart rate was recently discovered in the Pacific hagfish (Eptatretus stoutii): a soluble adenylyl cyclase (sAC)-mediated pathway that increases cyclic adenosine monophosphate (cAMP) production upon stimulation by HCO₃₋ to increase heart rate. However, still unknown is whether this cardiac control pathway is present in other species as well. The objective of my study was to determine the effects of increasing extracellular [HCO₃₋] on the in vitro cardiac function of other fish species and whether the sAC-mediated pathway is associated with recovery of cardiac function during debilitating conditions. Exposure to severe hypoxia (100% N₂) and hypercapnic acidosis (7.5% or 15% CO₂) significantly decreased the heart rate of isolated, freely beating hearts and reduced the isometric tension (contractility) of electrically paced ventricular strips from Pacific lamprey (Lampetra richardsoni), Pacific spiny dogfish (Squalus suckleyi), Asian swamp eel (Monopterus albus), white sturgeon (Acipenser transmontanus), zebrafish (Danio rerio), and starry flounder (Platichthys stellatus). Spontaneous recovery in heart rate or contractility was not observed during severe hypoxia or hypercapnic acidosis for any of the species tested. Addition of HCO₃₋ (up to 50 mM) was associated with a complete and dose-dependent recovery of control heart rate in lamprey, dogfish, and swamp eel hearts during severe hypoxia, and in dogfish, sturgeon, and swamp eel hearts during hypercapnic acidosis. A partial recovery of control heart rate was observed in lamprey and zebrafish hearts during hypercapnic acidosis. However, HCO₃₋ had no effect on the heart rate or contractility in flounder hearts and had little to no effect on restoring control contractility in dogfish, swamp eel, and flounder ventricular strips. The addition of KH7 (sAC blocker) abolished the HCO₃₋-induced recovery of heart rate during severe hypoxia only in the lamprey heart. Thus, the sAC-mediated pathway in cardiac control appears to be unique to the cyclostomes and not present in the other species tested. While the sAC-mediated pathway was associated with the recovery of heart rate in the lamprey heart, the specific mechanisms behind how HCO₃₋ was associated with the recovery of heart rate in the other species still needs to be determined.
Electric-field-induced reversible avalanche breakdown in a GaAs microcrystal due to cross band gap impact ionization
Creators: name: Klappenberger, Florian
name: Renk, Karl Friedrich
name: Summer, Raimund Franz
name: Keldysh, Leonid
name: Rieder, Bernhard
name: Wegscheider, Werner
Publisher: name: Universität Regensburg
Year: 2003
Subjects: subject: gallium arsenide, impact ionisation, avalanche breakdown, III-V semiconductors, electrical conductivity transitions, semiconductor switches, Gunn effect, electron-hole recombination
subject: 530 Physik
subject: 72.20.Ht; 77.22.Jp; 72.80.Ey; 72.60.+g; 72.20.Jv

description: We report on a reversible avalanche breakdown due to free-carrier multiplication caused by cross band gap impact ionization in a GaAs microcrystal. The n GaAs microcrystal (length 1 µm, diameter 1 µm) was embedded between n+ GaAs layers serving as electric contacts. We guided an electric pulse to the sample and determined, from the reflected and transmitted pulse, the I(V) characteristic. The breakdown was indicated by a sudden current rise and voltage drop and a hysteresis effect and, furthermore, by electron-hole recombination radiation. We reached the threshold field for ionization by making use of a high-field domain whose formation was based on the Gunn effect. The microcrystal could reproducibly be switched into the nonequilibrium avalanche state. Our analysis indicates that the effect provides a basis for the development of an ultrafast electric switch.
New Families of LDPC Block Codes Formed by Terminating Irregular Protograph-Based LDPC Convolutional Codes
Creators: name: Mitchell, David G. M.
name: Lentmaier, Michael
name: Costello, Daniel J.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Information Theory (cs.IT)
subject: FOS: Computer and information sciences

description: In this paper, we present a method of constructing new families of LDPC block code ensembles formed by terminating irregular protograph-based LDPC convolutional codes. Using the accumulate-repeat-by-4-jagged-accumulate (AR4JA) protograph as an example, a density evolution analysis for the binary erasure channel shows that this flexible design technique gives rise to a large selection of LDPC block code ensembles with varying code rates and thresholds close to capacity. Further, by means of an asymptotic weight enumerator analysis, we show that all the ensembles in this family also have minimum distance that grows linearly with block length, i.e., they are asymptotically good.
description: To be presented at the 2010 IEEE International Symposium on Information Theory
Gain spectra and current-induced change of refractice index in (In/Al)GaN diode lasers
Creators: name: Schwarz, Ulrich
name: Sturm, Evi
name: Wegscheider, Werner
name: Kümmler, V.
name: Lell, Alfred
name: Härle, Volker
Publisher: name: Universität Regensburg
Year: 2003
Subjects: subject: 530 Physik
subject: 42.55.Px; 42.60.Lh; 78.30.Fs

description: Adapting the Hakki-Paoli method for blue laser diodes we measure gain spectra for (In/Al)GaN on SiC substrate laser diodes in the low carrier density regime. From the measured longitudinal mode spacing we calculate the effective refractive index and can exclude a mode spacing anomaly. We demonstrate that the substrate has a considerable influence on the modal gain.
Medium Energy Ion Scattering of Gr on SiC(0001) and Si(100)
Creators: name: Copel, M.
name: Oida, S.
name: Kasry, A.
name: Bol, A. A.
name: Hannon, J. B.
name: Tromp, R. M.
Publisher: name: arXiv
Year: 2011
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: Depth profiling of graphene with high-resolution ion beam analysis is a practical method for analysis of monolayer thicknesses of graphene. Not only is the energy resolution sufficient to resolve graphene from underlying SiC, but by use of isotope labeling it is possible to tag graphene generated from reacted ethylene. Furthermore, we are able to analyze graphene supported by oxidized Si(100) substrates, allowing the study of graphene films grown by chemical vapor deposition on metal and transfered to silicon. This introduces a powerful method to explore the fundamentals of graphene formation.
Magnetotransport properties of arrays of cross-shaped antidots
Creators: name: Haan, S. de
name: Lorke, Axel
name: Henning, R.
name: Suhrke, Michael
name: Wegscheider, Werner
name: Bichler, Max
Publisher: name: Universität Regensburg
Year: 1999
Subjects: subject: 530 Physik
subject: 73.40.Kp, 05.60.Cd, 73.50.Jt

description: In magnetotransport measurements on arrays of cross-shaped antidots, we observe pronounced features in both the longitudinal and transverse magnetoresistivities ρxx and ρxy, which cannot be understood within the simple framework of commensurability between cyclotron radius and superlattice period. These resonances can be regarded as magnetotransport fingerprints of the complex unit cell. With the help of detailed numerical calculations using classical linear response theory we can ascribe additional maxima in ρxx to closed orbits in the dotlike potential between four antidots. A pronounced minimum in ρxy demonstrates the significance of open trajectories.
The Unification of Asymmetry Signatures of Type Ia Supernovae
Creators: name: Maund, J. R.
name: Hoeflich, P. A.
name: Patat, F.
name: Wheeler, J. C.
name: Zelaya, P.
name: Baade, D.
name: Wang, L.
name: Clocchiatti, A.
name: Quinn, J.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences

description: We present a compilation of the geometry measures acquired using optical and IR spectroscopy and optical spectropolarimetry to probe the explosion geometry of Type Ia SNe. Polarization measurements are sensitive to asymmetries in the plane of the sky, whereas line profiles in nebular phase spectra are expected to trace asymmetries perpendicular to the plane of the sky. The combination of these two measures can overcome their respective projection effects, completely probing the 3D structures of these events. For 9 normal Type Ia SNe, we find that the polarization of \ion{Si}{2} $λ6355$ at 5 days before maximum ($p_{Si\,II}$) is well correlated with its velocity evolution ($\dot{\rm v}_{Si\,II}$), implying $\dot{\rm v}_{Si\,II}$ is predominantly due to the asymmetry of the SNe. We find only a weak correlation between the polarization of \ion{Si}{2} and the reported velocities (${\rm v}_{neb}$) for peak emission of optical \ion{Fe}{2} and \ion{Ni}{2} lines in nebular spectra. Our sample is biased, with polarization measurements being only available for normal SNe which subsequently exhibited positive (i.e. redshifted) ${\rm v}_{neb}$. In unison these indicators are consistent with an off-centre delayed detonation, in which the outer layers are dominated by a spherical oxygen layer, mixed with an asymmetric distribution of intermediate mass elements. The combination of spectroscopic and spectropolarimetric indicators suggests a single geometric configuration for normal Type Ia SNe, with some of the diversity of observed properties arising from orientation effects.
description: 4 pages, 2 figures, ApJL subm
Spectral analysis on infinite Sierpinski fractafolds
Creators: name: Strichartz, Robert
name: Teplyaev, Alexander
Publisher: name: arXiv
Year: 2010
Subjects: subject: Functional Analysis (math.FA)
subject: Mathematical Physics (math-ph)
subject: Analysis of PDEs (math.AP)
subject: FOS: Mathematics
subject: FOS: Physical sciences
subject: 28A80, 31C25, 34B45, 60J45, 94C99

description: A fractafold, a space that is locally modeled on a specified fractal, is the fractal equivalent of a manifold. For compact fractafolds based on the Sierpinski gasket, it was shown by the first author how to compute the discrete spectrum of the Laplacian in terms of the spectrum of a finite graph Laplacian. A similar problem was solved by the second author for the case of infinite blowups of a Sierpinski gasket, where spectrum is pure point of infinite multiplicity. Both works used the method of spectral decimations to obtain explicit description of the eigenvalues and eigenfunctions. In this paper we combine the ideas from these earlier works to obtain a description of the spectral resolution of the Laplacian for noncompact fractafolds. Our main abstract results enable us to obtain a completely explicit description of the spectral resolution of the fractafold Laplacian. For some specific examples we turn the spectral resolution into a "Plancherel formula". We also present such a formula for the graph Laplacian on the 3-regular tree, which appears to be a new result of independent interest. In the end we discuss periodic fractafolds and fractal fields.
Growth and subband structure determination of high mobility hole gases on (0 0 1) and (1 1 0) GaAs
Creators: name: Gerl, Christian
name: Bauer, J.
name: Wegscheider, Werner
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: A1. Low-dimensional structures; A3. Molecular beam epitaxy; B2. Semiconducting galliumarsenide; B3. Heterojunction semiconductor devices
subject: 530 Physik
subject: 72.80.Ey; 73.21.Fg; 73.23.Ad; 73.43.Qt

description: We introduce high mobility two-dimensional hole systems (2DHSs) in AlGaAs/GaAs heterosystems grown by molecular beam epitaxy (MBE). Utilizing a carbon filament source, two-dimensional hole gases (2DHGs) were fabricated on the (0 0 1) and (1 1 0) crystal plan. These samples exhibit low-temperature mobilities beyond 106 cm2/V s at densities varying from 0.6 to 2.3×1011 cm−2. In order to explore the subband structure as a function of carrier density, aluminum top gates were deposited on the samples. The carrier density was found to show a hysteretic behavior when tuned with an external electric field. The origin of this effect will be discussed. It opens a way to adjust the hole density in a wide range within a single sample in the absence of an externally applied electric field.
GaMnAs grown on (0 0 1), (3 1 1) A and (1 1 0) GAaS substrates: Comparison of growth conditions and post-growth annealing behaviour
Creators: name: Wurstbauer, Ursula
name: Sperl, Matthias
name: Schuh, Dieter
name: Bayreuther, Günther
name: Sadowski, Janusz
name: Wegscheider, Werner
Publisher: name: Universität Regensburg
Year: 2007
Subjects: subject: A3. Molecular beam epitaxy; B1. GaMnAs; B2. Semiconducting III–IV materials; B3. Spintronic devices
subject: 530 Physik

description: Thin GaMnAs layers were grown by low temperature molecular beam epitaxy on (0 0 1), (3 1 1) A and (1 1 0) GaAs substrates. In an effort to increase the ferromagnetic transition temperature TC, we studied growth conditions and the effectiveness of post-growth annealing under an arsenic capping layer and in air. Avoiding As antisite defects with a small As to Ga flux ratio during MBE growth and reducing Mn interstitials by annealing the GaMnAs films in air for very long time at temperatures far below growth temperature allows us to obtain (0 0 1) samples with TC up to 150 K, (3 1 1) A samples with TC about of 110 K and (1 1 0) samples with TC of 89 K.