cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
Observations of the Binary Microlens Event MACHO-98-SMC-1 by the Microlensing Planet Search Collaboration
Creators: name: Rhie, S. H.
name: Becker, A. C.
name: Bennett, D. P.
name: Fragile, P. C.
name: Johnson, B. R.
name: King, L. J.
name: Peterson, B. A.
name: Quinn, J.
Publisher: name: arXiv
Year: 1998
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: We present the observations of the binary lensing event MACHO-98-SMC-1 conducted at the Mt.~Stromlo 74" telescope by the Microlensing Planet Search (MPS) collaboration. The MPS data constrain the first caustic crossing to have occurred after 1998 June 5.55 UT and thus directly rule out one of the two fits presented by the PLANET collaboration (model II). This substantially reduces the uncertainty in the the relative proper motion estimations of the lens object. We perform joint binary microlensing fits of the MPS data together with the publicly available data from the EROS, MACHO/GMAN and OGLE collaborations. We also study the binary lens fit parameters previously published by the PLANET and MACHO/GMAN collaborations by using them as initial values for $χ^2$ minimization. Fits based on the PLANET model I appear to be in conflict with the GMAN-CTIO data. From our best fit, we find that the lens system has a proper motion of $μ= 1.3\pm 0.2 \kmsk$ with respect to the source, which implies that the lens system is most likely to be located in the Small Magellanic Cloud strengthening the conclusion of previous reports.
description: 20 pages, 4 color figures
WHEN I THINK OF LEARNING ABOUT ASIA, … : STUDENTS’ VIEWS OF ASIA, AND THEIR MOTIVATIONS TOWARDS ASIA-RELATED LEARNING IN TWO AUSTRALIAN SECONDARY SCHOOLS
Creators: name: GARY JOHN BONAR
Publisher: name: Monash University
Year: 2019
Subjects: subject: Education
subject: 130106 Secondary Education
subject: FOS: Educational sciences
subject: 200314 South-East Asian Languages (excl. Indonesian)
subject: FOS: Languages and literature
subject: 160403 Social and Cultural Geography
subject: FOS: Social and economic geography

description: This study explored secondary students’ views of ‘Asia’, and motivations towards Asia-related learning. Survey, focus group, and Q-methodology factor analysis data showed that although students’ views of ‘Asia’ are complex, the influence of the Australia/Asia binary was prevalent. The factor analysis indicated five distinct perspectives. The perceived utility value of this learning was most prominent among these, though intrinsic interest and attainment value were also evident. With minimal existing data currently available on student attitudes, these results can inform the differentiation of Asia-related teaching in schools to achieve the objectives of the Asia and Australia’s engagement with Asia cross-curriculum priority.
Anomalous Floquet topological crystalline insulators
Creators: name: Ladovrechis, Konstantinos
name: Fulga, Ion Cosma
Publisher: name: arXiv
Year: 2018
Subjects: subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: FOS: Physical sciences

description: Periodically driven systems can host so called anomalous topological phases, in which protected boundary states coexist with topologically trivial Floquet bulk bands. We introduce an anomalous version of reflection symmetry protected topological crystalline insulators, obtained as a stack of weakly-coupled two-dimensional layers. The system has tunable and robust surface Dirac cones even though the mirror Chern numbers of the Floquet bulk bands vanish. The number of surface Dirac cones is given by a new topological invariant determined from the scattering matrix of the system. Further, we find that due to particle-hole symmetry, the positions of Dirac cones in the surface Brillouin zone are controlled by an additional invariant, counting the parity of modes present at high symmetry points.
description: 9 pages, 9 figures
Quantum Analog-Digital Conversion
Creators: name: Mitarai, Kosuke
name: Kitagawa, Masahiro
name: Fujii, Keisuke
Publisher: name: arXiv
Year: 2018
Subjects: subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: Many quantum algorithms, such as Harrow-Hassidim-Lloyd (HHL) algorithm, depend on oracles that efficiently encode classical data into a quantum state. The encoding of the data can be categorized into two types; analog-encoding where the data are stored as amplitudes of a state, and digital-encoding where they are stored as qubit-strings. The former has been utilized to process classical data in an exponentially large space of a quantum system, where as the latter is required to perform arithmetics on a quantum computer. Quantum algorithms like HHL achieve quantum speedups with a sophisticated use of these two encodings. In this work, we present algorithms that converts these two encodings to one another. While quantum digital-to-analog conversions have implicitly been used in existing quantum algorithms, we reformulate it and give a generalized protocol that works probabilistically. On the other hand, we propose an deterministic algorithm that performs a quantum analog-to-digital conversion. These algorithms can be utilized to realize high-level quantum algorithms such as a nonlinear transformation of amplitude of a quantum state. As an example, we construct a "quantum amplitude perceptron", a quantum version of neural network, and hence has a possible application in the area of quantum machine learning.
description: 7 pages
An IR Search for Extinguished Supernovae in Starburst Galaxies
Creators: name: Grossan, Bruce
name: Spillar, Earl
name: Tripp, Robert
name: Pirzkal, Norbert
name: Sutin, Brian M.
name: Johnson, Paul
Publisher: name: arXiv
Year: 1998
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: IR and Radio band observations of heavily extinguished regions in starburst galaxies suggest a very high SN rate associated with such regions. Optically measured supernova (SN) rates may therefore underestimate the total SN rate by factors of up to 10, due to the high extinction to SNe in starburst regions. The IR/radio SN rates come from a variety of indirect means, however, which suffer from model dependence and other problems. We describe a direct measurement of the SN rate from a regular patrol of starburst galaxies done with K' band imaging to minimize the effects of extinction. A collection of K' measurements of core-collapse SNe near maximum light is presented. Results of a preliminary SN search using the MIRC camera at the Wyoming IR Observatory (WIRO), and an improved search using the ORCA optics are described. A monthly patrol of starburst galaxies within 25 Mpc should yield 1.6 - 9.6 SNe/year. Our MIRC search with low-resolution (2.2" pixels) failed to find extinguished SNe, limiting the SN rate outside the nucleus (at > 15" radius) to less than 3.8 Supernova Rate Units (SRU or SNe/century/10^10 L(solar); 90% confidence). The MIRC camera had insufficient resolution to search nuclear starburst regions, where SN activity is concentrated, explaining why we found no heavily obscured SNe. We conclude that high-resolution, small field SN searches in starburst nuclei are more productive than low resolution, large-field searches, even for our large galaxies. With our ORCA high-resolution optics, we could limit the total SN rate to < 1.3 SRU at 90% confidence in 3 years of observations, lower than the most pessimistic estimate.
description: AJ Submitted 1998 Dec. 13. View figures and download all as one file at http://panisse.lbl.gov/public/bruce/irsn
Shelf-edge exchange in a numerical model of the Shetland shelf
Creators: name: Trivedi, Arjav
Publisher: name: Imperial College London
Year: 2017

description: The fast Shetland slope current flows on one side of the Faroe-Shetland Channel (FSC). Mesoscale activity and bottom friction are mechanisms that affect the slope current, helping to mix water and tracers across the shelf-edge. We simulate the FSC dynamics using a high resolution (~ 2km) hydrostatic configuration of the Massachusetts Institute of Technology General Circulation Model (MITgcm). The model was validated against a variety of observations: surface currents; Sea Surface Temperatures (SSTs); Acoustic Doppler Current Profilers (ADCPs); hydrographic observations; and shelf-edge exchange estimates. It is considered suitable for studying shelf-edge exchange here. We investigated bottom boundary layer (BBL) fluxes on the Shetland shelf. Fluxes near the shelf-edge are found to have a seasonal variability with high/low volume transport in winter/summer respectively. Using a multivariate regression approach, we find the locally wind-driven Ekman transport plays no explicit role in explaining daily bottom fluxes. We can better explain the variability of the across-slope BBL flux as a linear function of the speed and across-slope component of the interior flow, corresponding to an Ekman plus vertical-mean-flow flux. The spatial heterogeneity of the BBL fluxes is attributed to the vertical-mean-flow. We investigated meanders of the Shetland slope current. We develop a metric that characterises when the slope current meanders and use it to evaluate maps of the Potential Vorticity Anomalies (PVA). When the slope current meanders, there is a cyclone–anticyclone dipole and the PVA isolines bend. Inversely, when there is no meander, the PVA isolines are better aligned with the shelf. We additionally released tracers. When a meander exists, tracers released near the shelf spread extensively off it into the open ocean. When there is no meander, the tracers released on-/off-shelf remain on-/off-shelf. Daily correlations between our metric and the wind are poor, suggesting the genesis for meanders is not wind-driven.
Development of a multi keV x-ray backlighter source based on laser irradiation of extended cluster gases
Creators: name: Lowe, Hazel
Publisher: name: Imperial College London
Year: 2017

description: High intensity laser-cluster interactions have been studied for over two decades and have demonstrated extremely e fficient coupling of the incident laser energy to the high local density extended cluster medium, launching a strong radiative shock of interest for laboratory astrophysics studies. Laser-cluster interactions have also shown potential as a source of K-alpha emission. In this work, a long scale length (10 mm), high density (10^19 atoms/cm^3) cluster source has been commissioned to carry out a range of new experiments investigating the use of the extended hot plasma lament generated by the laser-cluster gas interaction as an x-ray source for x-ray back-lighting motivated by the low debris, high repetition rate nature of laser-cluster gas interactions. The first high intensity, ultra-short pulse (45 fs) laser interaction experiment with an extended Kr or Xe cluster medium at densities of 1017 atoms/cm£3 was carried out on the 12 J/45 fs Astra Gemini laser at a peak laser intensity of 10^19 W/cm^2. Up to 97% of the incident laser energy was absorbed by the cluster medium, generating free electron temperatures of 2.5-6 keV measured via a Ross pair continuum x-ray spectroscopy diagnostic. The hot plasma lament was imaged using an x-ray pinhole camera, showing a hollow x-ray structure with diameter greater than the initial laser-cluster interaction region, evincing radial energy transport before the peak in continuum emission was reached. The Alameda Applied Sciences Corporation (AASC) fast gas valve was deployed for the first time on a short pulse, high power laser experiment on the 500 mJ/500 fs Cerberus laser at Imperial College London, demonstrating point projection imaging with an x-ray source size of 150 micrometres above 2 keV in the direction of peak x-ray emission which was found to be along the laser axis on the laser entry side of the cluster gas volume. Up to 94% of the incident laser energy was absorbed by the Ar, Kr or Xe cluster medium producing free electron temperatures of 1-3 keV, with a resonance in heating seen at a cluster radius of 2.4 nm, measured by means of a single photon counting diagnostic. The x-ray conversion e ffciency from incident laser energy to emitted x-ray energy above 2 keV was estimated at 0.3%, corresponding to 1.5 mJ of emitted x-ray energy from the interaction. Optical probing of the interaction revealed two spatially separate regions in which the cluster medium was ionised on the rising edge of the pulse.
Beyond Bandit Feedback in Online Multiclass Classification
Creators: name: van der Hoeven, Dirk
name: Fusco, Federico
name: Cesa-Bianchi, Nicolò
Publisher: name: arXiv
Year: 2021
Subjects: subject: Machine Learning (cs.LG)
subject: FOS: Computer and information sciences

description: We study the problem of online multiclass classification in a setting where the learner's feedback is determined by an arbitrary directed graph. While including bandit feedback as a special case, feedback graphs allow a much richer set of applications, including filtering and label efficient classification. We introduce Gappletron, the first online multiclass algorithm that works with arbitrary feedback graphs. For this new algorithm, we prove surrogate regret bounds that hold, both in expectation and with high probability, for a large class of surrogate losses. Our bounds are of order $B\sqrt{ρKT}$, where $B$ is the diameter of the prediction space, $K$ is the number of classes, $T$ is the time horizon, and $ρ$ is the domination number (a graph-theoretic parameter affecting the amount of exploration). In the full information case, we show that Gappletron achieves a constant surrogate regret of order $B^2K$. We also prove a general lower bound of order $\max\big\{B^2K,\sqrt{T}\big\}$ showing that our upper bounds are not significantly improvable. Experiments on synthetic data show that for various feedback graphs, our algorithm is competitive against known baselines.
The Broad Line Radio Galaxy J2114+820
Creators: name: Lara, L.
name: Marquez, I.
name: Cotton, W. D.
name: Feretti, L.
name: Giovannini, G.
name: Marcaide, J. M.
name: Venturi, T.
Publisher: name: arXiv
Year: 1998
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: In the frame of the study of a new sample of large angular size radio galaxies selected from the NRAO VLA Sky Survey, we have made radio observations of J2114+820, a low power radio galaxy with an angular size of 6'. Its radio structure basically consists of a prominent core, a jet directed in north-west direction and two extended S-shaped lobes. We have also observed the optical counterpart of J2114+820, a bright elliptical galaxy with a strong unresolved central component. The optical spectrum shows broad emission lines. This fact, together with its low radio power and FR-I type morphology, renders J2114+820 a non-trivial object from the point of view of the current unification schemes of radio loud active galactic nuclei.
description: 6 pages, 5 figures. To appear in the proceedings of EVN/JIVE Symposium No. 4, New Astronomy Reviews (eds. Garrett et al.)
Atomic Layer Deposition of Yttrium Iron Garnet Thin Films for 3D Magnetic Structures
Creators: name: Lammel, M.
name: Scheffler, D.
name: Pohl, D.
name: Swekis, P.
name: Reitzig, S.
name: Reichlova, H.
name: Schlitz, R.
name: Geishendorf, K.
name: Siegl, L.
name: Rellinghaus, B.
name: Eng, L. M.
name: Nielsch, K.
name: Goennenwein, S. T. B.
name: Thomas, A.
Publisher: name: arXiv
Year: 2021
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: FOS: Physical sciences

description: A wide variety of new phenomena such as novel magnetization configurations have been predicted to occur in three dimensional magnetic nanostructures. However, the fabrication of such structures is often challenging due to the specific shapes required, such as magnetic tubes and spirals. Furthermore, the materials currently used to assemble these structures are predominantly magnetic metals that do not allow to study the magnetic response of the system separately from the electronic one. In the field of spintronics, the prototypical material used for such experiments is the ferrimagnetic insulator yttrium iron garnet (Y$_3$Fe$_5$O$_{12}$, YIG). YIG is one of the best materials especially for magnonic studies due to its low Gilbert damping. Here, we report the first successful fabrication of YIG thin films via atomic layer deposition. To that end we utilize a supercycle approach based on the combination of sub-nanometer thin layers of the binary systems Fe$_2$O$_3$ and Y$_2$O$_3$ in the correct atomic ratio on Y$_3$Al$_5$O$_{12}$ substrates with a subsequent annealing step. Our process is robust against typical growth-related deviations, ensuring a good reproducibility. The ALD-YIG thin films exhibit a good crystalline quality as well as magnetic properties comparable to other deposition techniques. One of the outstanding characteristics of atomic layer deposition is its ability to conformally coat arbitrarily-shaped substrates. ALD hence is the ideal deposition technique to grant an extensive freedom in choosing the shape of the magnetic system. The atomic layer deposition of YIG enables the fabrication of novel three dimensional magnetic nanostructures, which in turn can be utilized for experimentally investigating the phenomena predicted in those structures.
Charge recombination losses in non-fullerene acceptor based organic solar cells
Creators: name: Tan, Ching-Hong
Publisher: name: Imperial College London
Year: 2018

description: This thesis focuses on the factors determining the photocurrent generation efficiency of organic solar cells utilizing non-fullerene acceptors as opposed to the generally employed PCBM. This work explicates the photophysical properties of organic blends and devices incorporating such acceptors with transient absorption spectroscopy to understand their charge dynamics impact upon device performance and strategies to inhibit recombination detrimental to the photocurrent generation of such devices. The first results chapter introduces transient kinetic studies of a couple of promising blends with rhodanine based non-fullerene acceptors. These results show that the photocurrent generation in these acceptor blends is limited primarily by geminate recombination losses following efficient exciton separation and the losses are assigned to the difference in the nanomorphology of the blends. The next chapter reports an approach to suppress these losses in the device with non-fullerene acceptors: 1) An energetic offset increase is shown to suppress geminate recombination in blends with barbiturate acceptors, leading to a maximum EQE of ~84%. The third results chapter demonstrates a trade-off using a polymeric acceptor, N2200 which exhibits superior device thermal stability to PCBM based devices due to aggregation of PCBM upon thermal stress, but its initial device performance is limited by a geminate recombination and exciton decay to ground. The forth results chapter reports a comparison of charge generation for a series of non- fullerene acceptors blended with P3HT and PTB7-Th donors. A formation of an intermediate state prior to free dissociated charges is demonstrated to be bound polaron pair state and a high yield of such state is originated from the amorphous blend system. Geminate recombination losses suffered in the blend systems are suppressed by increasing the energy offset which in turn leads to an efficient photocurrent generation. The dissociation efficiency of bound-polaron pairs is shown to correlate with photocurrent generation efficiency. The last chapter provides concluding remarks and recommendations for further work.
Spatio-temporal Proper Orthogonal Decomposition of turbulent channel flow
Creators: name: Muralidhar, Srikanth Derebail
name: Podvin, Bérengère
name: Mathelin, Lionel
name: Fraigneau, Yann
Publisher: name: arXiv
Year: 2018
Subjects: subject: Fluid Dynamics (physics.flu-dyn)
subject: FOS: Physical sciences

description: An extension of Proper Orthogonal Decomposition is applied to the wall layer of a turbulent channel flow (Re τ = 590), so that empirical eigenfunctions are defined in both space and time. Due to the statistical symmetries of the flow, the igenfunctions are associated with individual wavenumbers and frequencies. Self-similarity of the dominant eigenfunctions, consistent with wall-attached structures transferring energy into the core region, is established. The most energetic modes are characterized by a fundamental time scale in the range 200-300 viscous wall units. The full spatio-temporal decomposition provides a natural measure of the convection velocity of structures, with a characteristic value of 12 u τ in the wall layer. Finally, we show that the energy budget can be split into specific contributions for each mode, which provides a closed-form expression for nonlinear effects.
The Lithium Plateau Enigma
Creators: name: Charbonnel, C.
name: Vauclair, S.
Publisher: name: arXiv
Year: 1998
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: Why is the lithium abundance constant in the so-called lithium plateau while all predictions suggest that it should vary from star to star? Can we find a "lithium attractor" which would remain stable in halo stars while fundamental parameters (M_*, Teff, [Fe/H]) vary?
description: Proceedings of "Galaxy evolution: Connecting the distant Universe with the local fossil record", Les Rencontres de l'Observatoire, Meudon, France, 1998
On the Atkinson formula for the $ζ$ function
Creators: name: Dona, Daniele
name: Alterman, Sebastian Zuniga
Publisher: name: arXiv
Year: 2021
Subjects: subject: Number Theory (math.NT)
subject: FOS: Mathematics
subject: 11M06, 11N37

description: Thanks to Littlewood (1922) and Ingham (1928), we know the first two terms of the asymptotic formula for the square mean integral value of the Riemann zeta function $ζ$ on the critical line. Later, Atkinson (1939) presented this formula with an error term of order $O(\sqrt{T}\log^{2}(T))$, which we call the Atkinson formula. Following the latter approach and the work of Titchmarsh (1986), we present an explicit version of the Atkinson formula, improving on a recent bound by Simonič (2020). Moreover, we extend the Atkinson formula to the range $\Re(s)\in\left[\frac{1}{4},\frac{3}{4}\right]$, giving an explicit bound for the square mean integral value of $ζ$ and improving on a bound by Helfgott and the authors (2019). We use mostly classical tools, such as the approximate functional equation and the explicit convexity bounds of the zeta function given by Backlund (1918).
description: 38 pages; v3: corrections and improvement on the order of the error term for Re(s)>1/2
Sublinear decoding schemes for non-adaptive group testing with inhibitors
Creators: name: Bui, Thach V.
name: Kuribayashi, Minoru
name: Kojima, Tetsuya
name: Echizen, Isao
Publisher: name: arXiv
Year: 2018
Subjects: subject: Information Theory (cs.IT)
subject: FOS: Computer and information sciences

description: Identification of up to $d$ defective items and up to $h$ inhibitors in a set of $n$ items is the main task of non-adaptive group testing with inhibitors. To efficiently reduce the cost of this Herculean task, a subset of the $n$ items is formed and then tested. This is called \textit{group testing}. A test outcome on a subset of items is positive if the subset contains at least one defective item and no inhibitors, and negative otherwise. We present two decoding schemes for efficiently identifying the defective items and the inhibitors in the presence of $e$ erroneous outcomes in time $\mathsf{poly}(d, h, e, \log_2{n})$, which is sublinear to the number of items $n$. This decoding complexity significantly improves the state-of-the-art schemes in which the decoding time is linear to the number of items $n$, i.e., $\mathsf{poly}(d, h, e, n)$. Moreover, each column of the measurement matrices associated with the proposed schemes can be nonrandomly generated in polynomial order of the number of rows. As a result, one can save space for storing them. Simulation results confirm our theoretical analysis. When the number of items is sufficiently large, the decoding time in our proposed scheme is smallest in comparison with existing work. In addition, when some erroneous outcomes are allowed, the number of tests in the proposed scheme is often smaller than the number of tests in existing work.
Training Discriminative Models to Evaluate Generative Ones
Creators: name: Lesort, Timothée
name: Stoain, Andrei
name: Goudou, Jean-François
name: Filliat, David
Publisher: name: arXiv
Year: 2018
Subjects: subject: Machine Learning (cs.LG)
subject: Machine Learning (stat.ML)
subject: FOS: Computer and information sciences

description: Generative models are known to be difficult to assess. Recent works, especially on generative adversarial networks (GANs), produce good visual samples of varied categories of images. However, the validation of their quality is still difficult to define and there is no existing agreement on the best evaluation process. This paper aims at making a step toward an objective evaluation process for generative models. It presents a new method to assess a trained generative model by evaluating the test accuracy of a classifier trained with generated data. The test set is composed of real images. Therefore, The classifier accuracy is used as a proxy to evaluate if the generative model fit the true data distribution. By comparing results with different generated datasets we are able to classify and compare generative models. The motivation of this approach is also to evaluate if generative models can help discriminative neural networks to learn, i.e., measure if training on generated data is able to make a model successful at testing on real settings. Our experiments compare different generators from the Variational Auto-Encoders (VAE) and Generative Adversarial Network (GAN) frameworks on MNIST and fashion MNIST datasets. Our results show that none of the generative models is able to replace completely true data to train a discriminative model. But they also show that the initial GAN and WGAN are the best choices to generate on MNIST database (Modified National Institute of Standards and Technology database) and fashion MNIST database.
Galactic cosmic rays and gamma rays: a unified approach
Creators: name: Strong, A. W.
name: Moskalenko, I. V.
Publisher: name: arXiv
Year: 1998
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: We are constructing a model which aims to reproduce observational data of many kinds related to cosmic-ray origin and propagation: direct measurements of nuclei, antiprotons, electrons and positrons, gamma-rays, and synchrotron radiation. These data provide many independent constraints on any model. Propagation of primary and secondary nucleons, primary and secondary electrons and positrons are calculated self-consistently. Fragmentation and energy losses are computed using realistic distributions for the interstellar gas and radiation fields, and diffusive reacceleration is also incorporated. The models are adjusted to agree with the observed cosmic-ray B/C and 10Be/9Be ratios. Our main results include evaluation of diffusion/convection and reacceleration models, estimates of the halo size, calculations of the interstellar positron and antiproton spectra, evaluation of alternative hypotheses of hard nucleon and hard electron interstellar spectra, and computation of the Galactic diffuse gamma-ray emission.
description: 21 pages including 19 ps-figures, latex, uses aaspp4.sty, epsfig.sty. To appear in "Topics in Cosmic Ray Astrophysics", ed. M. A. DuVernois, Nova Scientific: New York, 1999. More details can be found at http://www.gamma.mpe-garching.mpg.de/~aws/aws.html
Relativistic Distortions in the X-ray Spectrum of Cyg X-1
Creators: name: Done, Chris
name: Zycki, Piotr
Publisher: name: arXiv
Year: 1998
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: We present the first significant detection of relativistic smearing of the X-ray reflection spectrum from the putative accretion disk in the low/hard state of Cyg X-1. The ionization state, and amount of relativistic smearing are simultaneously constrained by the X-ray spectra, and we conclude that the disk is not strongly ionized, does not generally extend down to the last stable orbit at 3 Schwarzschild radii and covers rather less than half the sky as seen from the X-ray source. These results are consistent with a geometry where the optically thick disk truncates at a few tens of Schwarzschild radii, with the inner region occupied by the X-ray hot, optically thin(ish) plasma. Such a geometry is also inferred from previous studies of the reflected spectrum in Galactic Black Hole transient sources, and from detailed considerations of the overall continuum spectral shape, suggesting that this is a robust feature of low/hard state accretion onto Galactic Black Holes.
description: MNRAS, accepted by referee
A Path to Smart Radio Environments: An Industrial Viewpoint on Reconfigurable Intelligent Surfaces
Creators: name: Liu, Ruiqi
name: Wu, Qingqing
name: Di Renzo, Marco
name: Yuan, Yifei
Publisher: name: arXiv
Year: 2021
Subjects: subject: Networking and Internet Architecture (cs.NI)
subject: Information Theory (cs.IT)
subject: Signal Processing (eess.SP)
subject: FOS: Computer and information sciences
subject: FOS: Electrical engineering, electronic engineering, information engineering

description: With both the standardization and commercialization completed in an unforeseen pace for the 5th generation (5G) wireless network, researchers, engineers and executives from the academia and the industry have turned their sights on candidate technologies to support the next generation wireless networks. Reconfigurable intelligent surfaces (RIS), sometimes referred to as intelligent reflecting surfaces (IRS), have been identified to be potential components of the future wireless networks because they can reconfigure the propagation environment for wireless signals with low-cost passive devices. In doing so, the coverage of a cell can be expected to increase significantly as well as the overall throughput of the network. RIS has not only become an attractive research area but also triggered a couple of projects to develop appropriate solutions to enable the set-up of hardware demonstrations and prototypes. In parallel, technical discussions and activities towards standardization already took off in some regions. Promoting RIS to be integrated into future commercial networks and become a commercial success requires significant standardization work taken place both at regional level standards developing organizations (SDO) and international SDOs such as the 3rd Generation Partnership Project (3GPP). While many research papers study how RIS can be used and optimized, few effort is devoted to analyzing the challenges to commercialize RIS and how RIS can be standardized. This paper intends to shed some light on RIS from an industrial viewpoint and provide a clear roadmap to make RIS industrially feasible.
description: Submitted to IEEE Wireless Communications on April 27, 2021. Revised on July 29, 2021
Dust Formation Above Cool Magnetic Spots in Evolved Stars
Creators: name: Soker, Noam
name: Clayton, Geoffrey C.
Publisher: name: arXiv
Year: 1998
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: We examine the structure of cool magnetic spots in the photospheres of evolved stars, specifically asymptotic giant branch (AGB) stars and R Coronae Borealis stars. We find that the photosphere of a cool magnetic spot will be above the surrounding photosphere of AGB stars, opposite to the situation in the sun. This results from the behavior of the opacity, which increases with decreasing temperature, opposite to the behavior of the opacity near the effective temperature of the sun. We analyze the formation of dust above the cool magnetic spots, and suggest that the dust formation is facilitated by strong shocks, driven by stellar pulsations, which run through and around the spots. The presence of both the magnetic field and cooler temperatures make dust formation easier as the shock passes above the spot. We review some observations supporting the proposed mechanism, and suggest further observations to check the model.
description: 22 pages, uses aasms4.sty, preprint
Cardiac tissue engineering: how the physical properties of the scaffold affect the phenotype of naïve cardiomyocytes
Creators: name: Humphrey, Eleanor
Publisher: name: Imperial College London
Year: 2017

description: Human induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) are widely suggested as a suitable in vitro model for cardiac drug toxicity screening and for in vivo cardiac repair of damaged myocardium. However, the current immature phenotype of the iPSC-CMs limits their use in both these situations. Tissue engineering can promote in vitro maturation of iPSC-CMs towards a phenotype that is more representative of the human adult myocardium by using bioengineered matrices to provide elements associated with in vivo structure and function of native cardiac tissue, e.g. conductive or elastic polymers. However, the response of immature cardiomyocytes to some of these bioengineered constructs, serum albumin (SA) hydrogels, conductive polyaniline (PANI) scaffolds and biodegradable elastic polyhydroxyalkanoate (PHA) scaffolds, is unknown and hence investigated in this study. The bovine SA hydrogels are biocompatible and can be used to significantly increase the gene expression and significantly decrease the Ca2+ transient decay time of the neonatal rat ventricular myocytes (NRVMs), in comparison to NRVMs cultured on glass. The culture of NRVMs and fibroblasts on the SA hydrogels resulted in significantly slower Ca2+ cycling, but prolonged culture time in comparison to NRVMs alone. The bovine and human SA hydrogels can support the culture of iPSC-CMs for at least 28 days and the gene expression of the cells significantly increases with time in culture. The Ca2+ cycling is significantly faster in comparison to glass too. Conductive and non-conductive PANI scaffolds, coated with FBS proteins, are biocompatible with high NRVM and fibroblast adhesion and viability, which remain unchanged in comparison to glass. The NRVMs on the conductive PANI scaffolds have significantly faster Ca2+ transients and action potentials than those on the non-conductive PANI scaffolds, which suggest that the cells interact with the PANI scaffolds but the mechanism behind these changes is unknown and requires further investigation. PHA film scaffolds are biocompatible with iPSC-CMs and their blends may be used to manipulate cell properties to obtain tissue-engineered patches with significantly faster beating rate and Ca2+ influx. Sarcomere length remains unchanged, but comparable to adult myocardium. PHA aligned fibre scaffolds promote significantly increased cell alignment and significantly faster Ca2+ handling in iPSC-CMs, in comparison to randomly orientated PHA fibres, however further work is required to further optimise this and promote enhanced iPSC-CMs alignment to create a more biomimetic model. This thesis demonstrates the ability of different bioengineered constructs to manipulate the properties of immature cardiomyocytes with varying outcomes. Further work is required to produce functionally mature iPSC-CMs that are representative of native adult human myocardium.
Turbulence generated by multiscale inhomogeneous and anisotropic grids
Creators: name: Zheng, Shaokai
Publisher: name: Imperial College London
Year: 2017

description: In this thesis two classes of inhomogeneous multiscale grids are proposed and investigated experimentally. These studies provide further understandings of the idea to generate bespoke turbulence field using fractal grids as proposed by Vassilicos and colleagues. The first part of the work introduces the rectangular fractal grid (RFG). Due to the inhomogeneous grid geometry, the streamwise location of turbulence intensity peak appears different from the wake interaction length scale calculated from the grid bar dimensions, and a region of decreasing length scales with decreasing Reynolds number is observed. This region is shown to be inhomogeneous and anisotropic. Nevertheless, the non-equilibrium scaling is found in this region, where the ratio between the integral length scale and Taylor microscale remains constant. From the second part of the work, turbulent flows with different mean shear rates are studied using the new inhomogeneous multiscale grids. By designing the local blockage ratio and the bar dimensions, this new type of shear generating grid is capable of producing different mean velocity and turbulence intensity profiles at the same time. The mean velocity profiles are shown to match the predictive mean velocity model, and a scaling relation of turbulence intensity is proposed based on the wake interaction length scale. The streamwise evolution of the Reynolds stress is studied, and a new dimensionless time scale is proposed. Finally, the design and scaling methods of the turbulent shear flow generated by the inhomogeneous multiscale grid are tested in a low-fidelity engineering wind tunnel with different size and background flow quality, and the results are consistent. These results perhaps provide a general methodology to produce various types of turbulent flows through the design of one single passive grid, which is desirable for both fundamental studies of turbulence and engineering applications such as the wind engineering experiments.
L-series of harmonic Maass forms and a summation formula for harmonic lifts
Creators: name: Diamantis, Nikolaos
name: Lee, Min
name: Raji, Wissam
name: Rolen, Larry
Publisher: name: arXiv
Year: 2021
Subjects: subject: Number Theory (math.NT)
subject: FOS: Mathematics
subject: 11F67

description: We introduce an L-series associated with harmonic Maass forms and prove their functional equations. We establish converse theorems for these L-series and, as an application, we formulate and prove a summation formula for the holomorphic part of a harmonic lift of a given cusp form.
description: minor typos corrected
Supernova Remnant in a Stratified Medium: Explicit, Analytical Approximations for Adiabatic Expansion and Radiative Cooling
Creators: name: Maciejewski, Witold
name: Cox, Donald P.
Publisher: name: arXiv
Year: 1998
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: We propose simple, explicit, analytical approximations for the kinematics of an adiabatic blast wave propagating in an exponentially stratified ambient medium, and for the onset of radiative cooling, which ends the adiabatic era. Our method, based on the Kompaneets implicit solution and the Kahn approximation for the radiative cooling coefficient, gives straightforward estimates for the size, expansion velocity, and progression of cooling times over the surface, when applied to supernova remnants (SNRs). The remnant shape is remarkably close to spherical for moderate density gradients, but even a small gradient in ambient density causes the cooling time to vary substantially over the remnant's surface, so that for a considerable period there will be a cold dense expanding shell covering only a part of the remnant. Our approximation provides an effective tool for identifying the approximate parameters when planning 2-dimensional numerical models of SNRs, the example of W44 being given in a subsequent paper.
description: ApJ accepted, 11 pages, 2 figures embedded, aas style with ecmatex.sty and lscape.sty packages
Valley polarization of trions in monolayer MoSe$_2$ interfaced with bismuth iron garnet
Creators: name: Kravtsov, V.
name: Ivanova, T.
name: Abramov, A. N.
name: Shilina, P. V.
name: Kapralov, P. O.
name: Krizhanovskii, D. N.
name: Berzhansky, V. N.
name: Belotelov, V. I.
name: Shelykh, I. A.
name: Chernov, A. I.
name: Iorsh, I. V.
Publisher: name: arXiv
Year: 2021
Subjects: subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: Interfacing atomically thin van der Waals semiconductors with magnetic substrates enables additional control on their intrinsic valley degree of freedom and provides a promising platform for the development of novel valleytronic devices for information processing and storage. Here we study circularly polarized photoluminescence in heterostructures of monolayer MoSe$_2$ and thin films of ferrimagnetic bismuth iron garnet. We observe strong emission from charged excitons with negative valley polarization, which switches sign with increasing temperature, and demonstrate contrasting response to left and right circularly polarized excitation, associated with finite out-of-plane magnetization in the substrate. We propose a theoretical model accounting for magnetization-induced imbalance of charge carriers in the two valleys of MoSe$_2$, as well as for valley-switching scattering from B to A excitons and fast formation of trions with extended valley relaxation times, which shows excellent agreement with the experimental data. Our results provide new insights into valley physics in 2D semiconductors interfaced with magnetic substrates.
Intrinsic Absorption Lines in Seyfert 1 Galaxies. I. Ultraviolet Spectra from the Hubble Space Telescope
Creators: name: Crenshaw, D. Michael
name: Kraemer, Steven B.
name: Boggess, Albert
name: Maran, Stephen P.
name: Mushotzky, Richard F.
name: Wu, Chi-Chao
Publisher: name: arXiv
Year: 1998
Subjects: subject: Astrophysics (astro-ph)
subject: FOS: Physical sciences

description: We present a study of the intrinsic absorption lines in the ultraviolet spectra of Seyfert 1 galaxies. We find that the fraction of Seyfert 1 galaxies that show absorption associated with their active nuclei is more than one-half (10/17), which is much higher than previous estimates (3 - 10%) . There is a one-to-one correspondence between Seyferts that show intrinsic UV absorption and X-ray ``warm absorbers''. The intrinsic UV absorption is generally characterized by high ionization: C IV and N V are seen in all 10 Seyferts with detected absorption (in addition to Ly-alpha), whereas Si IV is present in only four of these Seyferts, and Mg II absorption is only detected in NGC 4151. The absorption lines are blueshifted (or in a few cases at rest) with respect to the narrow emission lines, indicating that the absorbing gas is undergoing net radial outflow. At high resolution, the absorption often splits into distinct kinematic components that show a wide range in widths (20 - 400 km/s FWHM), indicating macroscopic motions (e.g., radial velocity subcomponents or turbulence) within a component. The strong absorption components have cores that are much deeper than the continuum flux levels, indicating that the regions responsible for these components lie completely outside of the broad emission-line regions. The covering factor of the absorbing gas in the line of sight, relative to the total underlying emission, is C > 0.86, on average. The global covering factor, which is the fraction of emission intercepted by the absorber averaged over all lines of sight, is C > 0.5.
description: 56 pages, Latex, includes 4 figures (encapsulated postscript), Fig. 1 has 2 parts and Fig. 2 has 3 parts, to appear in the Astrophysical Journal
Stochastic modelling of soot in turbulent combustion
Creators: name: Schiener, Marcus Andreas
Publisher: name: Imperial College London
Year: 2017

description: The current work studies the modelling of soot in turbulent combustion via a sectional model, a two-equation type approach, and the method of moments with interpolative closure in the framework of a transported probability density function model closed at joint-scalar level. Detailed sectional model calculations in a premixed well-stirred/plug flow reactor system are carried out, and updates to nucleation rates for acetylene-based soot nucleation models and soot oxidation rates used in previous work are proposed and evaluated. The updates are integrated into two-equation and method of moments calculations of two turbulent non-premixed jet flames burning ethylene and a methane based fuel, and the sensitivity to the surface area dependance of soot growth and oxidation is evaluated. Further, soot volume fraction statistics and particle size distributions (PSDs) were calculated for the turbulent ethylene flame using the sectional soot model, and an improved agreement with experimental data over the two-equation model results was noted, while the calculated PSDs demonstrate the capabilities of the model. Overall, the current work presents a significant advance upon previously published results obtained using a wide range of alternative approaches.
Progressively Normalized Self-Attention Network for Video Polyp Segmentation
Creators: name: Ji, Ge-Peng
name: Chou, Yu-Cheng
name: Fan, Deng-Ping
name: Chen, Geng
name: Fu, Huazhu
name: Jha, Debesh
name: Shao, Ling
Publisher: name: arXiv
Year: 2021
Subjects: subject: Computer Vision and Pattern Recognition (cs.CV)
subject: FOS: Computer and information sciences

description: Existing video polyp segmentation (VPS) models typically employ convolutional neural networks (CNNs) to extract features. However, due to their limited receptive fields, CNNs can not fully exploit the global temporal and spatial information in successive video frames, resulting in false-positive segmentation results. In this paper, we propose the novel PNS-Net (Progressively Normalized Self-attention Network), which can efficiently learn representations from polyp videos with real-time speed (~140fps) on a single RTX 2080 GPU and no post-processing. Our PNS-Net is based solely on a basic normalized self-attention block, equipping with recurrence and CNNs entirely. Experiments on challenging VPS datasets demonstrate that the proposed PNS-Net achieves state-of-the-art performance. We also conduct extensive experiments to study the effectiveness of the channel split, soft-attention, and progressive learning strategy. We find that our PNS-Net works well under different settings, making it a promising solution to the VPS task.
description: MICCAI 2021 (Provisional accept); Code: https://github.com/GewelsJI/PNS-Net