cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
Holomorphic Couplings In Non-Perturbative String Compactifications
Creators: name: Klevers, Denis
Publisher: name: arXiv
Year: 2011
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: In this review article we present an analysis of several aspects of four-dimensional, non-perturbative N=1 compactifications of string theory. Our study focuses on brane dynamics and their effective physics as encoded in the holomorphic couplings of the low-energy N=1 effective action, most prominently the superpotential W. This article is divided into three parts. In part one we derive the effective action of a spacetime-filling D5-brane in generic Type IIB Calabi-Yau orientifold compactifications. In the second part we invoke tools from string dualities, namely from F-theory, heterotic/F-theory duality and mirror symmetry, for a more elaborate study of the dynamics of (p,q) 7-branes and heterotic five-branes. In this context we perform exact computations of the complete perturbative effective superpotential, both due to branes and background fluxes. Finally, in the third part we present a novel geometric description of five-branes in Type IIB and heterotic M-theory Calabi-Yau compactifications via a non-Calabi-Yau threefold, that is canonically constructed from the original five-brane and Calabi-Yau threefold via a blow-up. We use this blow-up threefold to derive open-closed Picard-Fuchs differential equations, that govern the complete effective brane and flux superpotential. In addition, we present first evidence to interpret the blow-up threefold as a flux compactification geometrically dual to the original five-brane by defining an SU(3)-structure on it, that is generated dynamically by the five-brane backreaction.
description: 300 pages, 5 figures; to be published in "Fortschritte der Physik"- Progress of Physics
Light trapping within the grooves of 1D diffraction gratings under monochromatic and sunlight illumination
Creators: name: Jakas, Mario M.
name: Llopis, Francisco
Publisher: name: arXiv
Year: 2011
Subjects: subject: Instrumentation and Detectors (physics.ins-det)
subject: Optics (physics.optics)
subject: FOS: Physical sciences

description: The Rayleigh-Modal method is used to calculate the electromagnetic field within the grooves of a perfectly conducting, rectangular-shaped 1D diffraction grating. An \emph{enhancement coefficient} ($η$) is introduced in order to quantify such an energy concentration. Accordingly, $η>$1 means that the amount of electromagnetic energy present within the grooves is larger than that one will have, over the same volume, if the diffraction grating is replaced by a perfectly reflecting mirror. The results in this paper show that $η$ can be as large as several decades at certain, often narrow, ranges of wavelengths. However, it reduces to approximately 20% under sunlight illumination. In this latter case, such values are achieved when the \textit{optical spacing} between the grooves $dn$ is greater than 500 nm, where $d$ is the groove spacing and $n$ is the refractive index of the substance within the grooves. For $dn$ smaller than 500 nm the enhancement coefficient turns negligibly small.
description: This paper contains 11 pages and 4 figures, and will be published elsewhere
Non-Abelian quantum order in spin-orbit-coupled semiconductors: The search for topological Majorana particles in solid state systems
Creators: name: Sau, Jay D.
name: Tewari, Sumanta
name: Lutchyn, Roman
name: Stanescu, Tudor
name: Sarma, S. Das
Publisher: name: arXiv
Year: 2010
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: FOS: Physical sciences

description: We show that an ordinary semiconducting thin film with spin-orbit coupling can, under ap- propriate circumstances, be in a quantum topologically ordered state supporting exotic Majorana excitations which follow non-Abelian statistics. The key to the quantum topological order is the coexistence of spin-orbit coupling with proximity-induced s-wave superconductivity and an externally-induced Zeeman coupling of the spins. For the Zeeman coupling below a critical value, the system is a non-topological (proximity-induced) s-wave superconductor. However, for a range of Zeeman coupling above the critical value, the lowest energy excited state inside a vortex is a zero-energy Majorana fermion state. The system, thus, has entered into a non-Abelian s-wave superconducting state via a topological quantum phase transition (TQPT) tuned by the Zeeman coupling. In the one-dimensional version of the same structure and for the Zeeman coupling above the critical value, there are localized Majorana zero-energy modes at the two ends of a semiconducting quantum nanowire. In this case, the Zeeman coupling can be induced more easily by an external magnetic field parallel to the wire, obviating the need for a magnetic insulator. We show that, despite the fact that the superconducting pair potential in the nanowire is explicitly s-wave, tunneling of electrons to the ends of the wire reveals a pronounced zero-bias peak. Such a peak is absent when the Zeeman coupling is below its critical value, i.e., the nanowire is in the non-topological s-wave superconducting state. We argue that the observation of this zero-bias tunneling peak in the semiconductor nanowire is possibly the simplest and clearest experiment proposed so far to unambiguously detect a Majorana fermion mode in a condensed matter system.
Multi-loop amplitudes in maximally supersymmetric pure spinor field theory
Creators: name: Bjornsson, Jonas
Publisher: name: arXiv
Year: 2010
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: This paper provides a more detailed background to the results of arXiv:1004.2692 concerning properties of multi-loop amplitudes in a pure spinor formulation of field theories with maximal supersymmetry. This involves the development of a first quantised field theory version of the non-minimal pure spinor formalism originally designed for describing superstring amplitudes. In addition to superspace world-line fields, the formalism involves a set of world-line ghost fields that are required for implementing BRST invariance with a composite b ghost. In particular, we show that BRST invariance requires the presence of certain contact terms. For four-point amplitudes, these are important beyond two loops. We also present an alternative proof of the "no-triangle hypothesis" and the vanishing of amplitudes with fewer than four external particles.
description: 65 pages, 15 figures
Las formas del duelo : memoria, utopía y visiones apocalípticas en las narrativas de la guerrilla mexicana (1979-2008)
Creators: name: Lara Aguilar, José Feliciano
Publisher: name: University of British Columbia
Year: 2016

description: This study analyzes six literary works of the Mexican contemporary guerrilla that covers the years 1979 to 2008: Al cielo por asalto (1979) by Agustín Ramos, ¿Por qué no dijiste todo? (1980) and La patria celestial (1992) by Salvador Castañeda, Morir de sed junto a la fuente. Sierra de Chihuahua 1968 (2001) by Minerva Armendáriz Ponce, Veinte de cobre (2004) by Fritz Glockner, and Vencer o morir (2008) by Leopoldo Ayala. In both their form and structure, these narratives address the notion of mourning, as well as its inherent categories, such as: work of mourning or grief work, melancholy, loss, grief, remnants, and specters, among others, which call into question and destabilize the generalized social discourse. In this tension, I observe the emergence of aesthetic languages that take place within the post-revolutionary imaginary of the 1960’s, and 1970’s with the exhaustion of revolutionary imaginary that was predominant in the preceding decades. These aesthetic languages provide mourning with new contents, organized in three fields: memory, utopia, and apocalyptic visions, which recreate mourning as a symbolic space where an important social struggle for the reconstruction of the past is still ongoing.
From SO/Sp instantons to W-algebra blocks
Creators: name: Hollands, Lotte
name: Keller, Christoph A.
name: Song, Jaewon
Publisher: name: arXiv
Year: 2010
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: Algebraic Geometry (math.AG)
subject: FOS: Physical sciences
subject: FOS: Mathematics

description: We study instanton partition functions for N=2 superconformal Sp(1) and SO(4) gauge theories. We find that they agree with the corresponding U(2) instanton partitions functions only after a non-trivial mapping of the microscopic gauge couplings, since the instanton counting involves different renormalization schemes. Geometrically, this mapping relates the Gaiotto curves of the different realizations as double coverings. We then formulate an AGT-type correspondence between Sp(1)/SO(4) instanton partition functions and chiral blocks with an underlying W(2,2)-algebra symmetry. This form of the correspondence eliminates the need to divide out extra U(1) factors. Finally, to check this correspondence for linear quivers, we compute expressions for the Sp(1)-SO(4) half-bifundamental.
description: 83 pages, 29 figures; minor changes
The Physical Model in Action: Quality Control for X-Shooter
Creators: name: Moehler, Sabine
name: Bristow, Paul
name: Kerber, Florian
name: Modigliani, Andrea
name: Vernet, Joel
Publisher: name: arXiv
Year: 2010
Subjects: subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: FOS: Physical sciences

description: The data reduction pipeline for the VLT 2nd generation instrument X-Shooter uses a physical model to determine the optical distortion and derive the wavelength calibration. The parameters of this model describe the positions, orientations, and other physical properties of the optical components in the spectrograph. They are updated by an optimisation process that ensures the best possible fit to arc lamp line positions. ESO Quality Control monitors these parameters along with all of the usual diagnostics. This enables us to look for correlations between inferred physical changes in the instrument and, for example, instrument temperature sensor readings.
description: 9 pages, 8 figures, style files included, Proc. of Observatory Operations: Strategies, Processes, and Systems III, eds. D.R. Silva, A.B. Peck, B.T. Soifer, SPIE 7737, 1G
Dark matter from dark energy-baryonic matter couplings
Creators: name: Aviles, Alejandro
name: Cervantes-Cota, Jorge L.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences

description: We present a scenario in which a scalar field dark energy is coupled to the trace of the energy momentum tensor of the baryonic matter fields. In the slow-roll regime, this interaction could give rise to the cosmological features of dark matter. We work out the cosmological background solutions and fit the parameters of the model using the Union 2 supernovae data set. Then, we develop the cosmological perturbations up to linear order, and we find that the perturbed variables have an acceptable behavior, in particular the density contrast of baryonic matter grows similar to that in the $Λ$CDM model for a suitable choice of the strength parameter of the coupling.
description: 10 pages, 8 figures, in this version small typos are corrected and it matches the published version in Phys. Rev. D15, January 2011
Hardy-Petrovitch-Hutchinson's problem and partial theta function
Creators: name: Kostov, Vladimir Petrov
name: Shapiro, Boris
Publisher: name: arXiv
Year: 2011
Subjects: subject: Classical Analysis and ODEs (math.CA)
subject: FOS: Mathematics
subject: Primary 30C15, Secondary 12D10, 26C05

description: In 1907 M.Petrovitch initiated the study of a class of entire functions all whose finite sections are real-rooted polynomials. An explicit description of this class in terms of the coefficients of a series is impossible since it is determined by an infinite number of discriminantal inequalities one for each degree. However, interesting necessary or sufficient conditions can be formulated. In particular, J.I.Hutchinson has shown that an entire function p(x)=a_0+a_1x+...+a_nx^n+... with strictly positive coefficients has the property that any its finite segment a_ix^i+...+a_jx^j has all real roots if and only if for all i=1,2,... one has a_i^2/a_{i-1}a_{i+1} is greater than or equal to 4. In the present paper we give sharp lower bounds on the ratios a_i^2/a_{i-1}a_{i+1} for the class considered by M.Petrovitch. In particular, we show that the limit of these minima when i tends to infinity equals the inverse of the maximal positive value of the parameter for which the classical partial theta function belongs to the Laguerre-Polya class.
De Sitter hunting in a classical landscape
Creators: name: Danielsson, Ulf H.
name: Haque, Sheikh S.
name: Koerber, Paul
name: Shiu, Gary
name: Van Riet, Thomas
name: Wrase, Timm
Publisher: name: arXiv
Year: 2011
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: We elaborate on the construction of de Sitter solutions from IIA orientifolds of SU(3)-structure manifolds that solve the 10-dimensional equations of motion at tree-level in the approximation of smeared sources. First we classify geometries that are orbifolds of a group manifold covering space which, upon the proper inclusion of O6 planes, can be described within the framework of N=1 supergravity in 4D. Then we scan systematically for de Sitter solutions, obtained as critical points of an effective 4D potential. Apart from finding many new solutions we emphasize the challenges in constructing explicit classical de Sitter vacua, which have sofar not been met. These challenges are interesting avenues for further research and include finding solutions that are perturbatively stable, satisfy charge and flux quantization, and have genuine localized (versus smeared) orientifold sources. This paper intends to be self-contained and pedagogical, and thus can serve as a guide to the necessary technical tools required for this line of research. In an appendix we explain how to study flux and charge quantization in the presence of a non-trivial H-field using twisted homology.
description: 50 pages, 3 figures
Holographic Dark Energy with Curvature
Creators: name: Cardenas, Victor H.
name: Perez, Roberto G.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences

description: In this paper we consider an holographic model of dark energy, where the length scale is the Hubble radius, in a non flat geometry. The model contains the possibility to alleviate the cosmic coincidence problem, and also incorporate a mechanism to obtain the transition from decelerated to an accelerated expansion regime. We derive an analytic form for the Hubble parameter in a non flat universe, and using it, we perform a Bayesian analysis of this model using SNIa, BAO and CMB data. We find from this analysis that the data favored a small value for $Ω_k$, however high enough to still produce cosmological consequences.
description: 6 pages, 2 figures
General Properties of Two-dimensional Conformal Transformation in Electrostatics
Creators: name: Zeng, Yong
name: Liu, Jinjie
name: Werner, Douglas H.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Classical Physics (physics.class-ph)
subject: FOS: Physical sciences

description: Electrostatic properties of two-dimensional nanosystems can be described by their geometry resonances. In this paper we prove that these modes as well as the corresponding eigenvalues are invariant under any conformal transformation. This invariance further leads to a new way to studying the transformed structures. Namely, transforming a geometry is equivalent to modifying the strengths of these invariant eigenmodes excited by the external excitations.
Systematic detection of magnetic fields in massive, late-type supergiants
Creators: name: Grunhut, Jason H.
name: Wade, Gregg A.
name: Hanes, David A.
name: Alecian, Evelyne
Publisher: name: arXiv
Year: 2010
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences

description: We report the systematic detection of magnetic fields in massive (M > 5 M$_\odot$) late-type supergiants, using spectropolarimetric observations obtained with ESPaDOnS at the Canada-France-Hawaii Telescope. Our observations reveal detectable Stokes V Zeeman signatures in Least-Squares Deconvolved mean line profiles in one-third of the observed sample of more than 30 stars. The signatures are sometimes complex, revealing multiple reversals across the line. The corresponding longitudinal magnetic field is seldom detected, although our longitudinal field error bars are typically 0.3 G ($1σ$). These characteristics suggest topologically complex magnetic fields, presumably generated by dynamo action. The Stokes V signatures of some targets show clear time variability, indicating either rotational modulation or intrinsic evolution of the magnetic field. We also observe a weak correlation between the unsigned longitudinal magnetic field and the CaII K core emission equivalent width of the active G2Iab supergiant $β$~Dra and the G8Ib supergiant $ε$~Gem.
description: 8 pages, 1 table, 6 figures, accepted for publication in MNRAS
Bulk and Surface Magnetization of Co atoms in Rutile Ti_[1-x]Co_xO_[2-delta] Thin Films Revealed by X-Ray Magnetic Circular Dichroism
Creators: name: Singh, V. R.
name: Sakamoto, Y.
name: Kataoka, T.
name: Kobayashi, M.
name: Yamazaki, Y.
name: Fujimori, A.
name: Chang, F. -H.
name: Huang, D. -J.
name: Lin, H. -J.
name: Chen, C. T.
name: Toyosaki, H.
name: Fukumura, T.
name: Kawasaki, M.
Publisher: name: arXiv
Year: 2011
Subjects: subject: Materials Science (cond-mat.mtrl-sci)
subject: FOS: Physical sciences

description: We have studied magnetism in Ti_[1-x]Co_xO_[2-δ] thin films with various x and δby soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L_[2,3] absorption edges. The estimated ferromagnetic moment by XMCD was 0.15-0.24 μβ/Co in the surface, while in the bulk it was 0.82-2.25 μβ/Co, which is in the same range as the saturation magnetization of 1.0-1.5 μβ/Co. Theseresults suggest that the intrinsic origin of the erromagnetism. The smaller moment of Co atom at surface is an indication of a magnetically dead layer of a few nm thick at the surface of the thin films.
description: This Paper is accepted in J. of Phys: Conds. Matter
Utilizing Astrometric Orbits to Obtain Coronagraphic Images
Creators: name: Davidson, John M.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: FOS: Physical sciences

description: We present an approach for utilizing astrometric orbit information to improve the yield of planetary images and spectra from a follow-on direct detection mission. This approach is based on the notion-strictly hypothetical-that if a particular star could be observed continuously, the instrument would in time observe all portions of the habitable zone so that no planet residing therein could be missed. This strategy could not be implemented in any realistic mission scenario. But if an exoplanet's orbit is known from astrometric observation, then it may be possible to plan and schedule a sequence of imaging observations that is the equivalent of continuous observation. A series of images-optimally spaced in time-could be recorded to examine contiguous segments of the orbit. In time, all segments would be examined, leading to the inevitable detection of the planet. In this paper, we show how astrometric orbit information can be used to construct such a sequence. Using stars from astrometric and imaging target lists, we find that the number of observations in this sequence typically ranges from 2 to 7, representing the maximum number of observations required to find the planet. The probable number of observations ranges from 1.5 to 3.1. This is a dramatic improvement in efficiency over previous methods proposed for utilizing astrometric orbits. We examine how the implementation of this approach is complicated and limited by operational constraints. We find that it can be fully implemented for internal coronagraph and visual nuller missions, with a success rate approaching 100%. External occulter missions will also benefit, but to a lesser degree.
description: 28 pages, 14 figures, submitted to PASP
Theory of mind, social cognition, and neural functioning in schizophrenia spectrum disorders
Creators: name: Burns, Amy Minh Nhat
Publisher: name: University of British Columbia
Year: 2016

description: Social cognitive functioning has been shown to be impaired in patients with schizophrenia (SZ), and these impairments are associated with functional outcomes. To better understand these deficits this dissertation investigated the neurocognitive processes associated with several social cognitive tasks. A novel irony comprehension paradigm was developed for use with electroencephalogram (EEG). The N400, a negative event related potential (ERP) that occurs 300-500 ms after the onset of a semantically incongruent word, and the P600, a positive ERP that occurs around 500-800 ms, were used to index irony comprehension. Study 1 revealed that SZ performed worse than healthy controls (HC) across three measures of social cognition – emotion perception, Theory of Mind (ToM), and irony comprehension. Furthermore, negative symptoms of SZ were associated with poor ToM performance. ERP findings showed that HC exhibited hemispheric differences in N400 amplitude in response to ironic sentences, with the left hemisphere showing smaller amplitudes to ironic compared to literal statements, whereas SZ did not show this differentiation. Although HC processed ironic statements differently compared to SZ, the direction of the effect was opposite of what was hypothesized. Study 2 examined the durability of this unanticipated finding in a larger group of HC. The N400 effect from Study 1was not replicated – there were no differences in N400 amplitude for ironic and literal statements. A difference in P600 was found whereby the P600 amplitude for literal was greater than for ironic. Self-reported schizotypal traits were associated with poor ToM performance. Study 3 examined whether computerized cognitive remediation (CCR), which has been shown to improve neurocognition, would generalize to social cognition, and whether these changes could be detected at a neural level using EEG. The CCR program implemented in this study produced no improvement in neurocognition or social cognition. Taken together, these results suggest that several aspects of social cognition are impaired in patients with schizophrenia, on a behavioural and possibly a neural level. Future studies are necessary to determine the most effective framework for CCR to minimize the deficits in interpersonal skills that are linked to both general cognitive abilities and social cognition in those with schizophrenia.
Quantum Anomalous Hall State in Bilayer Graphene
Creators: name: Nandkishore, Rahul
name: Levitov, Leonid
Publisher: name: arXiv
Year: 2010
Subjects: subject: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: FOS: Physical sciences

description: We present a symmetry-based analysis of competition between different gapped states that have been proposed in bilayer graphene (BLG), which are all degenerate on a mean field level. We classify the states in terms of a hidden SU(4) symmetry, and distinguish symmetry protected degeneracies from accidental degeneracies. One of the states, which spontaneously breaks discrete time reversal symmetry but no continuous symmetry, is identified as a Quantum Anomalous Hall (QAH) state, which exhibits quantum Hall effect at zero magnetic field. We investigate the lifting of the accidental degeneracies by thermal and zero point fluctuations, taking account of the modes softened under RG. Working in a 'saddle point plus quadratic fluctuations' approximation, we identify two types of RG- soft modes which have competing effects. Zero point fluctuations, dominated by 'transverse' modes which are unique to BLG, favor the QAH state. Thermal fluctuations, dominated by 'longitudinal' modes, favor a SU(4) symmetry breaking multiplet of states. We discuss the phenomenology and experimental signatures of the QAH state in BLG, and also propose a way to induce the QAH state using weak external magnetic fields.
description: minor changes, made to match journal version
Kerr-Schild Ansatz in Lovelock Gravity
Creators: name: Ett, Benjamin
name: Kastor, David
Publisher: name: arXiv
Year: 2011
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences

description: We analyze the field equations of Lovelock gravity for the Kerr-Schild metric ansatz, $g_{ab}=\bar g_{ab} +λk_ak_b$, with background metric $\bar g_{ab}$, background null vector $k^a$ and free parameter $λ$. Focusing initially on the Gauss-Bonnet case, we find a simple extension of the Einstein gravity results only in theories having a unique constant curvature vacuum. The field equations then reduce to a single equation at order $λ^2$. More general Gauss-Bonnet theories having two distinct vacua yield a pair of equations, at orders $λ$ and $λ^2$ that are not obviously compatible. Our results for higher order Lovelock theories are less complete, but lead us to expect a similar conclusion. Namely, the field equations for Kerr-Schild metrics will reduce to a single equation of order $λ^p$ for unique vacuum theories of order $p$ in the curvature, while non-unique vacuum theories give rise to a set of potentially incompatible equations at orders $λ^n$ with $1\le n \le p$. An examination of known static black hole solutions also supports this conclusion.
description: 14 pages; v2 reference added
Strongly correlated ultracold plasma
Creators: name: Sadeghi Esfahani, Hossein
Publisher: name: University of British Columbia
Year: 2016

description: Ultracold molecular plasmas represent a new frontier of plasma physics. They offer an easy and accessible laboratory for the study of strongly coupled Coulomb systems. Strong Coulomb coupling can give rise to exotic materials such as Wigner crystals and liquid like plasmas. In this thesis, I present a set of experiments and theoretical models that explore the properties of ultracold plasma in great detail. A supersonic beam of nitric oxide in helium creates a cold ensemble of ground state molecules. Upon two-color excitation, a Rydberg gas of nitric oxide evolves on a time scale of nanoseconds to form an ultracold plasma. The excited volume is imaged using a multichannel plate detector mounted on a movable grid. By moving the detector back and forth, we can observe the expansion dynamics of the plasma and its decay. Selective field ionization captures the relaxation of the Rydberg states to a plasma. We use a very reliable coupled-rate-equation model to understand the decay dynamics and evolution of Rydberg gas to a plasma by accounting for all the major processes that happen during the avalanche process. We find that a plasma evolved from an ultracold Rydberg gas expands very slowly, exhibits long relaxation time, and shows evidence suggesting the development of spatial order.
Spin equilibrium with or without gravitational wave emission: the case of XTE J1814-338 and SAX J1808.4-3658
Creators: name: Haskell, Brynmor
name: Patruno, Alessandro
Publisher: name: arXiv
Year: 2011
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: General Relativity and Quantum Cosmology (gr-qc)
subject: FOS: Physical sciences

description: In this letter we present a new analysis of the torques acting on the accreting millisecond X-ray pulsars SAX J1808.4-365 and XTE J1814-338, and show how our results can be used to constrain theoretical models of the spin evolution. In particular we find upper limits on any spin-up/down phase of XTE J1814-338 of $|\dotν|\lesssim\,1.5\times\,10^{-14}$ Hz/s at 95% confidence level. We examine the possibility that a gravitational wave torque may be acting in these systems and suggest that a more likely scenario is that both systems are close to spin equilibrium, as set by the disc/magnetosphere interaction.
description: Submitted to ApJ Letters
Collapse of Vacuum Bubbles in a Vacuum
Creators: name: Ng, Kin-Wang
name: Wang, Shang-Yung
Publisher: name: arXiv
Year: 2010
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: Motivated by the discovery of a plenitude of metastable vacua in a string landscape and the possibility of rapid tunneling between these vacua, we revisit the dynamics of a false vacuum bubble in a background de Sitter spacetime. We find that there exists a large parameter space that allows the bubble to collapse into a black hole or to form a wormhole. This may have interesting implications to inflationary physics.
description: 8 pages including 6 figures, LaTex; references added
Nondeterministic Amplifier for Two Photon Superpositions
Creators: name: Jeffers, John
Publisher: name: arXiv
Year: 2010
Subjects: subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences

description: We examine heralded nondeterministic noiseless amplification based on the quantum scissors device, which has been shown to increase the one-photon amplitude of a state at the expense of the vacuum-state amplitude. Here we propose using the same basic design to perform perfect amplification in a basis set of up to two photons. The device is much more efficient than several one-photon amplifiers working in tandem. When used to amplify coherent states this advantage is shown using either fidelity or in terms of probability of sucessful action, or more strikingly in a combination of the two.
description: References re-ordered, one added. Some typos corrected. Journal reference added. 8 pages, 10 figs
K 1-6: an asymmetric planetary nebula with a binary central star
Creators: name: Frew, David J.
name: Stanger, Jeff
name: Fitzgerald, Michael
name: Parker, Quentin
name: Danaia, Lena
name: McKinnon, David
name: Guerrero, Martín A.
name: Hedberg, John
name: Hollow, Robert
name: An, Yvonne
name: Bor, Shu Han
name: Colman, Isabel
name: Graham-White, Claire
name: Li, Qing Wen
name: Mai, Juliette
name: Papadakis, Katerina
name: Picone-Murray, Julia
name: Hoang, Melanie Vo
name: Yean, Vivian
Publisher: name: arXiv
Year: 2010
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences

description: We present new imaging data and archival multiwavelength observations of the little studied emission nebula K 1-6 and its central star. Narrow-band images in H-alpha (+ [NII]) and [OIII] taken with the Faulkes Telescope North reveal a stratified, asymmetric, elliptical nebula surrounding a central star which has the colours of a late G- or early K-type subgiant or giant. GALEX ultraviolet images reveal a very hot subdwarf or white dwarf coincident in position with this star. The cooler, optically dominant star is strongly variable with a period of 21.312 +/- 0.008 days, and is possibly a high amplitude member of the RS CVn class, although an FK Com classification is also possible. Archival ROSAT data provide good evidence that the cool star has an active corona. We conclude that K 1-6 is most likely an old bona fide planetary nebula at a distance of ~1.0 kpc, interacting with the interstellar medium, and containing a binary or ternary central star. The observations and data analyses reported in this paper were conducted in conjunction with Year 11 high school students as part of an Australian Research Council Linkage Grant science education project, denoted Space To Grow, conducted jointly by professional astronomers, educational researchers, teachers, and high-school students.
description: 13 pages, 5 figures, accepted by the Publications of the Astronomical Society of Australia (PASA)
Microwave studies on FeSe superconductors
Creators: name: Li, Meng
Publisher: name: University of British Columbia
Year: 2016

description: In this thesis, the microwave electrodynamic properties of stoichiometric FeSe are measured by a cavity perturbation technique based on a 940 MHz loop-gap resonator. Measurements surprisingly show, for the first time, that c-axis conductivity in stoichiometric FeSe superconductors exhibits a broad peak in its temperature-dependence, a phenomenon which was only observed for in-plane electrodynamics in the cuprates. This result implies that the charge transfer between FeSe-planes is enhanced by the development of long transport quasiparticle lifetimes below Tc.
Millimeter-wave study of London penetration depth temperature dependence in Ba(Fe0.926Co0.074)2As2 single crystal
Creators: name: Barannik, A. A.
name: Cherpak, N. T.
name: Ni, N.
name: Tanatar, M. A.
name: Vitusevich, S. A.
name: Skresanov, V. N.
name: Canfield, P. C.
name: Prozorov, R.
name: Glamazdin, V. V.
name: Torokhtii, K. I.
Publisher: name: arXiv
Year: 2011
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: Instrumentation and Detectors (physics.ins-det)
subject: FOS: Physical sciences

description: In-plane surface Ka-band microwave impedance of optimally doped single crystals of the Fe-based superconductor Ba(Fe0.926Co0.074)2As2 (Tc= 22.8K) was measured. Sensitive sapphire disk quasi-optical resonator with high-Tc cuprate conducting endplates was developed specially for Fe-pnictide superconductors. It allowed finding temperature variation of London penetration depth in a form of power law, namely Δλ(T)~ Tn with n = 2.8 from low temperatures up to at least 0.6Tc consisted with radio-frequency measurements. This exponent points towards nodeless state with pairbreaking scattering, which can support one of the extended s-pairing symmetries. The dependence λ(T) at low temperatures is well described by one superconducting small-gap (Δ\cong 0.75 in kTc units, where k is Boltzman coefficient) exponential dependence.
description: 6 pages, 2 figures, to be published in Low Temperature Physics,vol.37, August 2011
Pauli graphs when the Hilbert space dimension contains a square: why the Dedekind psi function ?
Creators: name: Planat, Michel
Publisher: name: arXiv
Year: 2010
Subjects: subject: Mathematical Physics (math-ph)
subject: Group Theory (math.GR)
subject: Number Theory (math.NT)
subject: Quantum Physics (quant-ph)
subject: FOS: Physical sciences
subject: FOS: Mathematics

description: We study the commutation relations within the Pauli groups built on all decompositions of a given Hilbert space dimension $q$, containing a square, into its factors. Illustrative low dimensional examples are the quartit ($q=4$) and two-qubit ($q=2^2$) systems, the octit ($q=8$), qubit/quartit ($q=2\times 4$) and three-qubit ($q=2^3$) systems, and so on. In the single qudit case, e.g. $q=4,8,12,...$, one defines a bijection between the $σ(q)$ maximal commuting sets [with $σ[q)$ the sum of divisors of $q$] of Pauli observables and the maximal submodules of the modular ring $\mathbb{Z}_q^2$, that arrange into the projective line $P_1(\mathbb{Z}_q)$ and a independent set of size $σ(q)-ψ(q)$ [with $ψ(q)$ the Dedekind psi function]. In the multiple qudit case, e.g. $q=2^2, 2^3, 3^2,...$, the Pauli graphs rely on symplectic polar spaces such as the generalized quadrangles GQ(2,2) (if $q=2^2$) and GQ(3,3) (if $q=3^2$). More precisely, in dimension $p^n$ ($p$ a prime) of the Hilbert space, the observables of the Pauli group (modulo the center) are seen as the elements of the $2n$-dimensional vector space over the field $\mathbb{F}_p$. In this space, one makes use of the commutator to define a symplectic polar space $W_{2n-1}(p)$ of cardinality $σ(p^{2n-1})$, that encodes the maximal commuting sets of the Pauli group by its totally isotropic subspaces. Building blocks of $W_{2n-1}(p)$ are punctured polar spaces (i.e. a observable and all maximum cliques passing to it are removed) of size given by the Dedekind psi function $ψ(p^{2n-1})$. For multiple qudit mixtures (e.g. qubit/quartit, qubit/octit and so on), one finds multiple copies of polar spaces, ponctured polar spaces, hypercube geometries and other intricate structures. Such structures play a role in the science of quantum information.
description: 18 pages, version submiited to J. Phys. A: Math. Theor
title: Zwischen Raubgut, Fremddarstellungen und menschlichen Überresten. Sammlungsstrategien und sensible Objekte
Creators: name: Kreft, Anika
Publisher: name: ZZF - Centre for Contemporary History: Visual History
Year: 2020

description: Viele Aborigines und Torres-Strait-Insulaner*innen vermeiden Darstellungen von kürzlich Verstorbenen in Filmen oder auf Fotos sowie die Nennung ihrer Namen. Dies gilt als schmerzhaft und respektlos den Angehörigen gegenüber und könnte den Übergangsprozess des Toten ins Jenseits stören. Ob und wie lange diese Vermeidungsgebote bis hin zu Darstellungs- und Nennungsverboten angewandt werden, ist abhängig von den unterschiedlichen Communities der First Australians sowie individuellen ethischen Vorstellungen von Angehörigen. Das australische Nationalarchiv entschied sich bei der digitalen Präsentation seiner Film- und Fotosammlung für den oben erwähnten Warnhinweis – um der Verletzung von Gefühlen vorzubeugen und Respekt gegenüber den kulturellen Werten der Aborigines und Torres-Strait-Insulaner*innen auszudrücken. Die Abbildungen von verstorbenen First Australians würden einige Wissenschaftler*innen als „kulturell sensibel“ bezeichnen. Wie gehen andere Archive, Museen, Universitäten und weitere Institutionen mit sensiblen Bildern und Objekten in ihren Sammlungen um? Was sind Problemfelder und Lösungsansätze? Transparenz und Partizipation sind zwei zentrale Stichworte hinsichtlich des Umgangs mit sensiblen Objekten in Sammlungen.
Wess-Zumino term in the N=4 SYM effective action revisited
Creators: name: Belyaev, Dmitry V.
name: Samsonov, Igor B.
Publisher: name: arXiv
Year: 2011
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: FOS: Physical sciences

description: The low-energy effective action for the N=4 super Yang-Mills on the Coulomb branch is known to include an SO(6)-invariant Wess-Zumino (WZ) term for the six scalar fields. For each maximal, non-anomalous subgroup of the SU(4) R-symmetry, we find a four-dimensional form of the WZ term with this subgroup being manifest. We then show that a recently proposed expression for the four-derivative part of the effective action in N=4 USp(4) harmonic superspace yields the WZ term with manifest SO(5) R-symmetry subgroup. The N=2 SU(2) harmonic superspace form of the effective action produces the WZ term with manifest SO(4) x SO(2). We argue that there is no four-dimensional form of the WZ term with manifest SU(3) R-symmetry, which is relevant for N=1 and N=3 superspace formulations of the effective action.
description: 26 pages; minor corrections and improvements
Characterization of interactions for BtuB, Colicin E3, and HslT
Creators: name: Mills, Allan
Publisher: name: University of British Columbia
Year: 2016

description: The outer membrane of Gram-negative bacteria acts as a physical barrier against the dangers of the extracellular environment. The outer membrane contains a number of porins and transporters to facilitate the import of nutrients while simultaneously protecting cells from extracellular assault. How these proteins transport nutrients and how they can be subverted are still areas of investigation. In the first study the mechanisms of transport through the vitamin B₁₂ transporter BtuB is investigated. BtuB was found to interact in a 1:1 molar ratio with the inner membrane protein TonB, which is required for transport of vitamin B₁₂ (cobalamin). Binding of TonB, in turn, alters the binding dynamics of the ligand with BtuB and slows the dissociation of ligand. In the second study transport of the antimicrobial protein colicin E3 across the outer membrane was investigated. Colicin E3 is a ribosomal nuclease that exists in a complex with an inhibitor, immunity protein Im3. Denaturation of colicin E3 was found to facilitate the interaction of the colicin with its outer membrane binding partners by dissociation of Im3. Release of Im3 from colicin E3 allows the nuclease domain of colicin E3 to interact with lipopolysaccharide as part of the transport process. Finally, OmpC and HslT from the Gram-negative Salmonella enterica serovar Typhimurium are hypothesized to interact to protect persistent infectious cells from the oxidizing assault of the immune system. No direct interaction between OmpC and HslT was detectable, possible explanations for this lack of interaction are discussed. These results are discussed in the context of how both ligands and antimicrobial compounds are transported across the outer membrane.
Nonperturbative QED Effective Action at Finite Temperature
Creators: name: Kim, Sang Pyo
name: Lee, Hyun Kyu
name: Yoon, Yongsung
Publisher: name: arXiv
Year: 2010
Subjects: subject: High Energy Physics - Theory (hep-th)
subject: General Relativity and Quantum Cosmology (gr-qc)
subject: High Energy Physics - Phenomenology (hep-ph)
subject: Nuclear Theory (nucl-th)
subject: FOS: Physical sciences

description: We advance a novel method for the finite-temperature effective action for nonequilibrium quantum fields and find the QED effective action in time-dependent electric fields, where charged pairs evolve out of equilibrium. The imaginary part of the effective action consists of thermal loops of the Fermi-Dirac or Bose-Einstein distribution for the initial thermal ensemble weighted with factors for vacuum fluctuations. And the real part of the effective action is determined by the mean number of produced pairs, vacuum polarization, and thermal distribution. The mean number of produced pairs is equal to twice the imaginary part. We explicitly find the finite-temperature effective action in a constant electric field.
description: RevTex4, 6pages, no figure; replaced by the version to be published in Phys. Rev. D
Unitary and Non-Unitary Matrices as a Source of Different Bases of Operators Acting on Hilbert Spaces
Creators: name: Filippov, S. N.
name: Man'ko, V. I.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Quantum Physics (quant-ph)
subject: Mathematical Physics (math-ph)
subject: FOS: Physical sciences

description: Columns of d^2 x N matrices are shown to create different sets of N operators acting on $d$-dimensional Hilbert space. This construction corresponds to a formalism of the star-product of operator symbols. The known bases are shown to be partial cases of generic formulas derived by using d^2 x N matrices as a source for constructing arbitrary bases. The known examples of the SIC-POVM, MUBs, and the phase-space description of qubit states are considered from the viewpoint of the developed unified approach. Star-product schemes are classified with respect to associated d^2 x N matrices. In particular, unitary matrices correspond to self-dual schemes. Such self-dual star-product schemes are shown to be determined by dequantizers which do not form POVM.
description: 12 pages, 1 figure, 1 table, to appear in Journal of Russian Laser Research
Additional file 1 of Assessing a novel modelling approach with high resolution UAV imagery for monitoring health status in priority riparian forests
Creators: name: Guerra-Hernández, Juan
name: Díaz-Varela, Ramón A.
name: Ávarez-González, Juan Gabriel
name: Rodríguez-González, Patricia María
Publisher: name: figshare
Year: 2021
Subjects: subject: Medicine
subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: Ecology
subject: FOS: Biological sciences
subject: Sociology
subject: FOS: Sociology
subject: 69999 Biological Sciences not elsewhere classified
subject: 80699 Information Systems not elsewhere classified
subject: FOS: Computer and information sciences
subject: Plant Biology

description: Additional file 1: Table 1. Estimated parameters, standard errors (SE), z values statistics and p-values for the model logit1 predicting the probability that the tree belongs to category A. Table 2. Estimated parameters, standard errors (SE), z values statistics and p-values for the model logit2 predicting whether mortality will occur in a tree. Table 3. Estimated parameters, standard errors (SE), z values statistics and p-values for the logit3 model predicting whether mortality will occur in a tree.
An Over-the-Air Reconfiguration API for Experimental Cognitive Radio Setups
Creators: name: Fischer, Moritz
name: Braun, Martin
name: Elsner, Jens P.
name: Jondral, Friedrich K.
Publisher: name: Karlsruhe
Year: 2011

description: We present a software solution for over-the-air reconfiguration of remote software radio terminals using the free GNU Radio toolkit, facilitating the development of Cognitive Radio applications. The modular architecture allows for separating the cognitive engine from the signal processing algorithms, thus allowing fast implementation, veriﬁcation and easier testing.
Lower Bounds on the Success Probability for ad hoc Networks with local FDMA scheduling
Creators: name: Tanbourgi, Ralph
name: Elsner, Jens P.
name: Jäkel, Holger
name: Jondral, Friedrich K.
Publisher: name: Karlsruhe
Year: 2011

description: This paper studies the performance of ad hoc networks with local FDMA scheduling using stochastic point processes. In such networks, the Poisson assumption is not justified due to interdependencies between points introduced by scheduling. For this reason, an upper bound on the second reduced moment measure is derived. Using this result, two lower bounds on the success probability are given, based on the second order product density and a non-homogeneous Poisson approximation. The relative performance of local FDMA is compared to random channel access. It is shown that the relative outage probability reduction of local FDMA highly depends on the SIR threshold as well as on the ratio of transmission distance to orthogonalization distance. If these two quantities are small, the improvement is high; the number of channels has only a minor effect on the relative improvement.
Superconductivity-induced optical anomaly in an iron arsenide
Creators: name: Charnukha, A.
name: Popovich, P.
name: Matiks, Y.
name: Sun, D. L.
name: Lin, C. T.
name: Yaresko, A. N.
name: Keimer, B.
name: Boris, A. V.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Superconductivity (cond-mat.supr-con)
subject: Strongly Correlated Electrons (cond-mat.str-el)
subject: FOS: Physical sciences

description: One of the central tenets of conventional theories of superconductivity, including most models proposed for the recently discovered iron-pnictide superconductors, is the notion that only electronic excitations with energies comparable to the superconducting energy gap are affected by the transition. Here we report the results of a comprehensive spectroscopic ellipsometry study of a high-quality crystal of superconducting $\textrm{Ba}_{0.68}\textrm{K}_{0.32}\textrm{Fe}_2\textrm{As}_2$ that challenges this notion. We observe a superconductivity-induced suppression of an absorption band at an energy of $2.5\ \textrm{eV}$, two orders of magnitude above the superconducting gap energy $2Δ\sim 20\ \textrm{meV}$. Based on density-functional calculations, this band can be assigned to transitions from As-p to Fe-d orbitals crossing the Fermi surface. We identify a related effect at the spin-density-wave transition in parent compounds of the 122 family. This suggests that As-p states deep below the Fermi level contribute to the formation of the superconducting and spin-density-wave states in the iron arsenides.
description: 5 pages, 3 figures. Supplementary material: 6 pages, 3 figures (1 interactive)