cometadata/datacite-rtg-text-other-reclassification-records huggingface dataset:
Development of an innovative modular steel truss system
Creators: name: Zhuo, Sirou
Publisher: name: University of British Columbia
Year: 2018

description: This thesis proposes an innovative and economical modular steel truss system (MSTS), using modular steel floor system (MSFS) and modular buckling restrained braced truss moment frame (MBRBTMF). The proposed MSTS can be fabricated offsite and then shipped and assembled on site, saving construction time and fabrication expense. This specially designed floor system, MSFS, consists of space trusses and precast concrete slab toppings, and to fully utilize the spaces within the floors, the mechanical, electrical and plumbing (MEP) systems are pre-installed within. The proposed floor system was optimized for both gravity and lateral loads, using a robust structural optimization method conducted in conjunction with the Matlab and OpenSees. Space trusses are utilized to provide sufficient stiffness to support gravity, eliminate vertical deflection and transfer lateral force without significantly increasing floor depth. The buckling restrained braces (BRBs) in MBRBTMF are employed as energy dissipation components, allowing the structures to be repaired efficiently after earthquakes. The seismic performances of a MSTS structure and conventional structures with MSFS were systematically analyzed with OpenSees. The nonlinear dynamic responses of these structures show that the proposed modular system is highly efficient in resisting gravity and lateral loads, and can be used efficiently for modular constructions worldwide.
Option Pricing Driven by Lévy Processes
Creators: name: Xiang, Peiwen
Publisher: name: The Australian National University
Year: 2020
Subjects: Option Pricing
Lévy Processes
Stochastic Processes

description: The methodology of pricing financial derivatives, particularly stock options, was first introduced by Bachelier and developed by Black, Scholes and Merton, who gave the explicit formula for option pricing. Recent developed models such as jump-diffusion, Heston and Variance Gamma are also widely studied within the quantitative finance field and are proven to be applicable to a certain degree in real markets. A brief understanding of option pricing with stochastic processes is given in this thesis. Risk neutral valuation and notion of finding an equivalent martingale measure provide a framework under which derivatives are priced. Basic procedures of constructing a Brownian motion and stochastic integral from fundamental blocks are introduced. Infinitely divisible distributions and Lévy processes are detailedly discussed, including Lévy-Itô decomposition and the notion of subordination. Exponential-Lévy model and Fourier transform methods are presented to illustrate different approaches to option pricing. Simulation of AAPL stock prices based on estimated parameters from historical data under jump diffusion model is compared with empirical data to test the fitness of the model. Stock prices by minimal measure and Esscher transform measure are computed under geometric Lévy processes. Finally, univariate Variance Gamma process model is extended to Sato's two factor model for multivariate option pricing. The focus of this thesis is to give a detailed analysis of different option pricing models using mathematical and statistical concepts and theories, accompanied with simulations and empirical data to test the fitness of models. Extensions to numerous popular models are also discussed.
Spin filter effects in mesoscopic ring structures
Creators: name: Popp, Markus
name: Frustaglia, Diego
name: Richter, Klaus
Publisher: name: Universität Regensburg
Year: 2003
Subjects: subject: 530 Physik

description: We study the spin-dependent conductance of ballistic mesoscopic ring systems in the presence of an inhomogeneous magnetic field. We show that, for the set-up proposed, even a small Zeeman splitting can lead to a considerable spin polarization of the current. Making use of a spin-switch effect (Frustaglia et al2001 Phys. Rev. Lett. 87 256602) we propose a device of two rings connected in series that in principle allows for both creating and coherently controlling spin polarized currents at low temperatures.
Single vortex-antivortex pair in an exciton polariton condensate
Creators: name: Roumpos, Georgios
name: Fraser, Michael D.
name: Löffler, Andreas
name: Höfling, Sven
name: Forchel, Alfred
name: Yamamoto, Yoshihisa
Publisher: name: arXiv
Year: 2010
Subjects: subject: Quantum Gases (cond-mat.quant-gas)
subject: FOS: Physical sciences

description: In a homogeneous two-dimensional system at non-zero temperature, although there can be no ordering of infinite range, a superfluid phase is predicted for a Bose liquid. The stabilization of phase in this superfluid regime is achieved by the formation of bound vortex-antivortex pairs. It is believed that several different systems share this common behaviour, when the parameter describing their ordered state has two degrees of freedom, and the theory has been tested for some of them. However, there has been no direct experimental observation of the phase stabilization mechanism by a bound pair. Here we present an experimental technique that can identify a single vortex-antivortex pair in a two-dimensional exciton polariton condensate. The pair is generated by the inhomogeneous pumping spot profile, and is revealed in the time-integrated phase maps acquired using Michelson interferometry, which show that the condensate phase is only locally disturbed. Numerical modelling based on open dissipative Gross-Pitaevskii equation suggests that the pair evolution is quite different in this non-equilibrium system compared to atomic condensates. Our results demonstrate that the exciton polariton condensate is a unique system for studying two-dimensional superfluidity in a previously inaccessible regime.
Manuscript Data
Creators: name: Boyd-Meredith, Tyler
Publisher: name: figshare
Year: 2021
Subjects: Neuroscience

description: FOF recordings from 5 rats performing a dynamic evidence accumulation task. These recordings yielded 738 units from these 5 rats. Data was collected using unilateral electrode arrays (n=4) and bilateral tetrodes (n=1). Each rat has an accompanying behavioral dataset containing an average of 108,126 trials performing the dynamic clicks task. These trials were used to fit a previously described accumulation model to their behavior (Piet et al, 2018). The dynamic clicks task presents the animal with two streams of randomly-timed auditory clicks on the left and right side of a central fixation port. These left and right click trains are generated with at a high rate (38Hz) on one side and a low rate (2Hz) on the other. The underlying click rates alternate a rate of 1Hz and the rat is rewarded for correctly identifying the side generating the higher click rate at the end of the trial. To solve this task, rats learn to discount older evidence so that the most recently presented clicks have the greatest effect on the decision. This induces changes of mind throughout each trial, which we can predict with our behavioral model and relate to neural activity.
This dataset, along with the accompanying code (https://github.com/Brody-Lab/dynamic_ephys) can be used to regenerate all the results and figures in the manuscript titled Stable choice coding in FOF across model predicted changes of mind (Boyd-Meredith and Piet et al., under review; preprint here: https://www.biorxiv.org/content/10.1101/2021.05.13.444020v2).
Behavioral data:Each rat (H###) has behavioral data saved in a file titled data/H###.matThis contains a matlab struct called data with fields like:T - the duration of the trialleftbups - the timing of the left clicks relative to stimulus onset in each trialpokedR - boolean indicated whether the rat went to the rightward portsessid - a unique identifier for each sessiongenSwitchTimes - the timing of the state switches relative to the stimulus onset on that trial
Model fits:Each rat's accumulation model fits are saved in a file titled results/fit_analytical_H###.matThis contains a matlab struct with fields like:final - the best fit parameters to the accumulation modelparam_names - the names associated with each parameterauto_se - standard error derived from automatic differentiation in julia
Electrophysiology data:
Each cell has an associated file titled: data/phys/bin/phys_data_#####.matThis file contains an associated ratname and sessid as well as a struct array of length ntrials called array_data whose fields are things likestim_start - the timing (in seconds) of the stimulus start relative to the beginning of the trialspikes - the timing of the spikes on the trial
The easiest way to begin working with the data is to clone the accompanying git repository https://github.com/Brody-Lab/dynamic_ephys
Fingerprints of mesoscopic leads in the conductance of a molecular wire
Creators: name: Cuniberti, Gianaurelio
name: Fagas, Giorgos
name: Richter, Klaus
Publisher: name: Universität Regensburg
Year: 2002
Subjects: subject: Carbon nanotubes; Electronic transport; Green functions
subject: 530 Physik

description: The influence of contacts on linear transport through a molecular wire attached to mesoscopic tubule leads is studied. It is shown that low dimensional leads, such as carbon nanotubes, in contrast to bulky electrodes, strongly affect transport properties. By focusing on the specificity of the lead-wire contact, we show, in a fully analytical treatment, that the geometry of this hybrid system supports a mechanism of channel selection and a sum rule, which is a distinctive hallmark of the mesoscopic nature of the electrodes.
Integrated photonic quantum gates for polarization qubits
Creators: name: Crespi, Andrea
name: Ramponi, Roberta
name: Osellame, Roberto
name: Sansoni, Linda
name: Bongioanni, Irene
name: Sciarrino, Fabio
name: Vallone, Giuseppe
name: Mataloni, Paolo
Publisher: name: arXiv
Year: 2011
Subjects: subject: Quantum Physics (quant-ph)
subject: Optics (physics.optics)
subject: FOS: Physical sciences

description: Integrated photonic circuits have a strong potential to perform quantum information processing. Indeed, the ability to manipulate quantum states of light by integrated devices may open new perspectives both for fundamental tests of quantum mechanics and for novel technological applications. However, the technology for handling polarization encoded qubits, the most commonly adopted approach, is still missing in quantum optical circuits. Here we demonstrate the first integrated photonic Controlled-NOT (CNOT) gate for polarization encoded qubits. This result has been enabled by the integration, based on femtosecond laser waveguide writing, of partially polarizing beam splitters on a glass chip. We characterize the logical truth table of the quantum gate demonstrating its high fidelity to the expected one. In addition, we show the ability of this gate to transform separable states into entangled ones and vice versa. Finally, the full accessibility of our device is exploited to carry out a complete characterization of the CNOT gate through a quantum process tomography.
description: 6 pages, 4 figures
On interpretation of recent proper motion data for the Large Magellanic Cloud
Creators: name: Bekki, Kenji
Publisher: name: arXiv
Year: 2011
Subjects: subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences

description: Recent observational studies using the Hubble Space Telescope (HST) have derived the center-of-mass proper motion (CMPM) of the Large Magellanic Cloud (LMC). Although these studies carefully treated both rotation and perspective effects in deriving the proper motion for each of the sampled fields, they did not consider the effects of local random motion in the derivation. This means that the average PM of the fields (i.e., the observed CMPM) could significantly deviate from the true CMPM, because the effect of local random motion can not be close to zero in making the average PM for the small number of the fields (~10). We discuss how significantly the observationally derived CMPM can deviate from the true CMPM by applying the same method as used in the observations for a dynamical model of the LMC with a known true CMPM. We find that the deviation can be as large as ~ 50 km/s (~0.21 mas/yr), if the LMC has a thick disk and a maximum circular velocity of ~120$ km/s. We also find that the deviation depends both on the total number of the sampled fields and on structure and kinematics of the LMC. We therefore suggest that there is a possibility that the observed CMPM of the LMC deviates from the true one to some extent. We also show that a simple mean of PM for a large number of the LMC fields (~1000) can be much closer to the true CMPM.
description: 12 pages, 4 figures accepted in ApJL
Supporting random wave models: a quantum mechanical approach
Creators: name: Urbina, Juan Diego
name: Richter, Klaus
Publisher: name: Universität Regensburg
Year: 2003
Subjects: subject: 530 Physik
subject: 05.45.Mt
subject: 05.40.−a

description: We show how two-point correlation functions recently derived within non-isotropic random wave models can be obtained in the appropriate limit in terms of the exact Green function of the quantum system. Since no statistical model is required for this derivation, this shows that taking the wavefunctions as Gaussian processes is the only assumption of those models. We also show how for clean systems the two-point correlation function based on an energy average defines a Gaussian theory which substantially reduces the spurious contributions coming from the normalization problem.
Ionospheric Power-Spectrum Tomography in Radio Interferometry
Creators: name: Koopmans, L. V. E.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Instrumentation and Methods for Astrophysics (astro-ph.IM)
subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: Astrophysics of Galaxies (astro-ph.GA)
subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences

description: A tomographic method is described to quantify the three-dimensional power-spectrum of the ionospheric electron-density fluctuations based on radio-interferometric observations by a two-dimensional planar array. The method is valid to first-order Born approximation and might be applicable to correct observed visibilities for phase variations due to the imprint of the full three-dimensional ionosphere. It is shown that not the ionospheric electron density distribution is the primary structure to model in interferometry, but its autocorrelation function or equivalent its power-spectrum. An exact mathematical expression is derived that provides the three dimensional power-spectrum of the ionospheric electron-density fluctuations directly from a rescaled scattered intensity field and an incident intensity field convolved with a complex unit phasor that depends on the w-term and is defined on the full sky pupil plane. In the limit of a small field of view, the method reduces to the single phase screen approximation. Tomographic self-calibration can become important in high-dynamic range observations at low radio frequencies with wide-field antenna interferometers, because a three-dimensional ionosphere causes a spatially varying convolution of the sky, whereas a single phase screen results in a spatially invariant convolution. A thick ionosphere can therefore not be approximated by a single phase screen without introducing errors in the calibration process. By applying a Radon projection and the Fourier projection-slice theorem, it is shown that the phase-screen approach in three dimensions is identical to the tomographic method. Finally we suggest that residual speckle can cause a diffuse intensity halo around sources, due to uncorrectable ionospheric phase fluctuations in the short integrations, which could pose a fundamental limit on the dynamic range in long-integration images.
description: 8 pages; Accepted for publication in ApJ
Quantum chaos in optical systems: The annular billiard
Creators: name: Hentschel, Martina
name: Richter, Klaus
Publisher: name: Universität Regensburg
Year: 2002
Subjects: subject: 530 Physik
subject: 05.45.Mt
subject: 03.65.Sq
subject: 42.25.-p
subject: 42.60.Da

description: We study the dielectric annular billiard as a quantum chaotic model of a micro-optical resonator. It differs from conventional billiards with hard-wall boundary conditions in that it is partially open and composed of two dielectric media with different refractive indices. The interplay of reflection and transmission at the different interfaces gives rise to rich dynamics of classical light rays and to a variety of wave phenomena. We study the ray propagation in terms of Poincaré surfaces of section and complement it with full numerical solutions of the corresponding wave equations. We introduce and develop an S-matrix approach to open optical cavities which proves very suitable for the identification of resonances of intermediate width that will be most important in future applications like optical communication devices. We show that the Husimi representation is a useful tool in characterizing resonances and establish the ray-wave correspondence in real and phase space. While the simple ray picture provides a good qualitative description of certain system classes, only the wave description reveals the quantitative details.
Acoustic Power Absorption and its Relation with Vector Magnetic Field of a Sunspot
Creators: name: Gosain, S.
name: Mathew, S. K.
name: Venkatakrishnan, P.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences

description: The distribution of acoustic power over sunspots shows an enhanced absorption near the umbra--penumbra boundary. Earlier studies revealed that the region of enhanced absorption coincides with the region of strongest transverse potential field. The aim of this paper is to (i) utilize the high-resolution vector magnetograms derived using Hinode SOT/SP observations and study the relationship between the vector magnetic field and power absorption and (ii) study the variation of power absorption in sunspot penumbrae due to the presence of spine-like radial structures. It is found that (i) both potential and observed transverse fields peak at a similar radial distance from the center of the sunspot, and (ii) the magnitude of the transverse field, derived from Hinode observations, is much larger than the potential transverse field derived from SOHO/MDI longitudinal field observations. In the penumbra, the radial structures called spines (intra-spines) have stronger (weaker) field strength and are more vertical (horizontal). The absorption of acoustic power in the spine and intra-spine shows different behaviour with the absorption being larger in the spine as compared to the intra-spine.
description: 18 pages, 7 figures, In Press Solar Physics, Topical Issue on Helio-and-Astroseismology
Theory of an all-carbon molecular switch
Creators: name: Gutiérrez, Rafael
name: Fagas, Giorgos
name: Cuniberti, Gianaurelio
name: Grossmann, Frank
name: Schmidt, Rüdiger
name: Richter, Klaus
Publisher: name: Universität Regensburg
Year: 2002
Subjects: subject: 530 Physik
subject: 73.63.Fg
subject: 61.46.+w
subject: 71.15.Ap
subject: 72.80.Rj

description: We study electron transport across a carbon molecular junction consisting of a C60 molecule sandwiched between two semi-infinite metallic carbon nanotubes. It is shown that the Landauer conductance of this carbon hybrid system can be tuned within orders of magnitude not only by varying the tube-C60 distance, but more importantly at fixed distances by (i) changing the orientation of the Buckminsterfullerene or (ii) rotating one of the tubes around its cylinder axis. Furthermore, it is explicitly shown that structural relaxation determines qualitatively the transmission spectrum of such devices.
The skill of mental health
Creators: name: Leder, Garson Titeff
Publisher: name: University of British Columbia
Year: 2020

description: Psychotherapy is effective. Since the 1970's, meta-analyses have consistently shown a significant effect size for psychotherapeutic interventions when compared to no treatment or placebo treatments. This effectiveness is normally taken as a sign of the scientific legitimization of clinical psychotherapy. A significant problem, however, is that most psychotherapies appear to be equally effective. This poses a problem for specific psychotherapies: they may work, but likely not for the reasons that ground their theoretical explanations for their effectiveness. This dissertation explains the common efficacy of psychotherapies by developing novel skill-based account of mental illness and healing. According to the view defended here, mental illness, and the success of mental healing, is best explained as an issue of the breakdown and development of skilled action. This skill view of mental health attempts to resolve a number of long-standing metaphysical questions about the roles of biological dysfunction, the environment, and values in the conception of mental disorder.
Parametric frequency tuning of phase-locked nano-electromechanical resonators
Creators: name: Kraus, Andreas
name: Erbe, Artur
name: Corso, Gilberto
name: Richter, Klaus
name: Blick, Robert H.
Publisher: name: Universität Regensburg
Year: 2001
Subjects: subject: 530 Physik

description: We present measurements on nanoelectromechanical systems fabricated in semiconductor materials suited for operating frequencies in the radio band. We demonstrate how to achieve parametric frequency tuning of nanoelectromechanical resonators required for radio frequency sensor and communication applications.
Classical and quantum periodically driven scattering in one dimension
Creators: name: Henseler, Michael
name: Dittrich, Thomas
name: Richter, Klaus
Publisher: name: Universität Regensburg
Year: 2001
Subjects: subject: 530 Physik

description: Irregular scattering at harmonically driven one- dimensional potential wells is studied both on the classical and the quantum level. We show that an ac-driven single square well, and a smooth well with oscillating bottom, are sufficient to generate chaotic scattering. For a square well with oscillating bottom, we introduce the concept of pseudointegrable scattering. The quantum dynamics of these models is treated using Floquet scattering theory, which is exact for arbitrary amplitude and frequency of the driving. In the deep quantum regime, scattering is dominated by multiphoton exchanges with the driving field, leading to complex resonance structures in transmission and reflection. For strong and fast driving, the ac-driven square well develops an effective double-well potential that introduces coherent tunneling in the scattering. We identify signatures of classical chaotic scattering in a phase-space representation of the quantum dynamics.
Ballistic Weak Localization in Classically Chaotic Antidot Arrays: Influence of Geometric Factors
Creators: name: Richter, Klaus
name: Hennig, Ralf
name: Suhrke, Michael
name: Yevtushenko, Oleg
Publisher: name: Universität Regensburg
Year: 2000
Subjects: subject: Weak localization; Antidot arrays
subject: 530 Physik

description: We address weak localization (WL) of electrons in a two-dimensional ballistic classically chaotic billiard of antidots. According to a recent proposal ballistic WL is sensitive to the transport relaxation and phase-coherence times as well as to the Ehrenfest time {\it t$_{E}$} and to the Lyapunov exponent {\it lambda} of the classical system. This results in a non-trivial effect of the geometrical parameters of the antidots on the quantum WL correction to the classical magnetoconductivity. We analyze this phenomenon in detail and discuss how {\it t$_{E }$} and {\it lambda} can in principle be determined from conductivity measurements.
On Shanks' Algorithm for Modular Square Roots
Creators: name: Schlage-Puchta, Jan-Christoph
Publisher: name: arXiv
Year: 2011
Subjects: subject: Number Theory (math.NT)
subject: FOS: Mathematics
subject: 11Y16

description: Let $p$ be a prime number, $p=2^nq+1$, where $q$ is odd. D. Shanks described an algorithm to compute square roots $\pmod{p}$ which needs $O(\log q + n^2)$ modular multiplications. In this note we describe two modifications of this algorithm. The first needs only $O(\log q + n^{3/2})$ modular multiplications, while the second is a parallel algorithm which needs $n$ processors and takes $O(\log q+n)$ time.
The ABC of Digital Business Ecosystems
Creators: name: Stanley, Jo
name: Briscoe, Gerard
Publisher: name: arXiv
Year: 2010
Subjects: subject: Computers and Society (cs.CY)
subject: FOS: Computer and information sciences

description: The European Commission has the power to inspire, initiate and sponsor huge transnational projects to an extent impossible for most other entities. These projects can address universal themes and develop well-being models that are valuable across a diversity of societies and economies. It is a universal fact that SMEs in all countries provide a substantial proportion of total employment, and conduct much of a nation's innovative activity. Yet these smaller companies struggle in global markets on a far from level playing field, where large companies have distinct advantages. To redress this imbalance the Commission saw it as a priority to improve the trading capability of the Small and Medium-sized Enterprises (SMEs), and perceived digital platforms as the modern means to this end. They considered that the best operational model for a vibrant Web2.0-based Internet services industry would be by analogy to well-performing biological ecosystems. Open Source Software is adopted in the DBE/OPAALS projects as the best support for sustainability of such complex electronic webs, since it minimises interoperability problems, enables code access for cheaper in-house modification or development of systems, and reduces both capital and operating expenditure.
description: 24 pages, 5 figures
Mechanical Mixing in Nonlinear Nanomechanical Resonators
Creators: name: Erbe, A.
name: Corso, G.
name: Krommer, H.
name: Tilke, A.
name: Richter, Klaus
name: Blick, Robert
Publisher: name: Universität Regensburg
Year: 2000
Subjects: subject: 530 Physik

description: The physics of nonlinear dynamics has been studied in detail in macroscopic mechanical systems like the driven classical pendulum. By now, it is possible to build mechanical devices on the nanometer scale with eigenfrequencies on the order of several 100 MHz. In this work, we want to present how to machine such nanomechanical resonators out of silicon-on-insulator wafers and how to operate them in the nonlinear regime in order to investigate higher-order mechanical mixing at radio frequencies. The nonlinear response then is compared in detail to nth-order perturbation theory and nonperturbative numerical calculations.
An estimate for Frobenius' diophantine problem in three dimensions
Creators: name: Schlage-Puchta, Jan-Christoph
Publisher: name: arXiv
Year: 2011
Subjects: subject: Number Theory (math.NT)
subject: FOS: Mathematics
subject: 11D04

description: We give upper and lower bounds for the largest integer not representable as positive linear combination of three given integers, disproving an upper bound conjectured by Beck, Einstein and Zacks.
Analyzing Color Information of Scanned Maps
Creators: name: Rümmler, Arne
name: Figgemeier, Heiko
name: Ott, Nikolas
Publisher: name: Zenodo
Year: 2023

description: Presentation of team HUeL|O163, which participated in Challenge 2: Inspection of color information in scanned raster maps of the Dataxplorers Hackathon 2023. The presented approach analyzes the images' color information in the CIELab color space. The developed software is available and documented at GitHub.
Weak Localization in Antidot Arrays: Signature of Classical Chaos
Creators: name: Yevtushenko, Oleg
name: Lütjering, Gerd
name: Weiss, Dieter
name: Richter, Klaus
Publisher: name: Universität Regensburg
Year: 2000
Subjects: subject: 530 Physik

description: We study, experimentally and theoretically, quantum weak localization (WL) corrections to the classical magnetoconductivity of two-dimensional ballistic systems with regular and disordered patterns of dense antidots. We analyze the observed temperature and flux dependences of the WL using different theoretical models for the chaotic dynamics and dephasing rates. The measured resistivity curves, which deviate from those of diffusive systems, reflect chaotic motion and correlations in the classical dynamics of electrons in the antidot landscape. The results support the significance of the Ehrenfest time as a relevant time scale for ballistic WL.
Addition Spectra of Chaotic Quantum Dots: Interplay between Interactions and Geometry
Creators: name: Ahn, Kang-Hun
name: Richter, Klaus
name: Lee, In-Ho
Publisher: name: Universität Regensburg
Year: 1999
Subjects: subject: 530 Physik

description: We investigate the influence of interactions and geometry on ground states of clean chaotic quantum dots using the self-consistent Hartree-Fock method. We find two distinct regimes of interaction strength: While capacitive energy fluctuations {\it delta chi} follow approximately a random matrix prediction for weak interactions, there is a crossover to a regime where {\it delta chi} is strongly enhanced and scales roughly with interaction strength. This enhancement is related to the rearrangement of charges into ordered states near the quantum dot edge. This effect is nonuniversal depending on the shape and the size of the dot. It may provide insight into recent experiments on statistics of Coulomb blockade peak spacings.
From clean to diffusive mesoscopic systems: A semiclassical approach to the magnetic susceptibility
Creators: name: McCann, Edward
name: Richter, Klaus
Publisher: name: Universität Regensburg
Year: 1998
Subjects: subject: 530 Physik

description: We study disorder-induced spectral correlations and their effect on the magnetic susceptibility of mesoscopic quantum systems in the non-diffusive regime. By combining a diagrammatic perturbative approach with semiclassical techniques we perform impurity averaging for non-translational invariant systems. This allows us to study the crossover from clean to diffusive systems. As an application we consider the susceptibility of non-interacting electrons in a ballistic microstructure in the presence of weak disorder. We present numerical results for a square billiard and approximate analytic results for generic chaotic geometries. We show that for the elastic mean free path {\it l } larger than the system size, there are two distinct regimes of behaviour depending on the relative magnitudes of {\it l} and an inelastic scattering length.
Statistics of Coulomb Blockade Peak Spacings within the Hartree-Fock Approximation
Creators: name: Cohen, Avraham
name: Richter, Klaus
name: Berkovits, Richard
Publisher: name: Universität Regensburg
Year: 1999
Subjects: subject: 530 Physik

description: We study the effect of electronic interactions on the addition spectra and on the energy-level distributions of two-dimensional quantum dots with weak disorder using the self-consistent Hartree- Fock approximation for spinless electrons. We show that the distribution of the conductance peak spacings is Gaussian with large fluctuations that exceed, in agreement with experiments, the mean level spacing of the noninteracting system. We analyze this distribution on the basis of Koopmans' theorem. We show furthermore that the occupied and unoccupied Hartree-Fock levels exhibit Wigner-Dyson statistics.
The Expected Perimeter in Eden and Related Growth Processes
Creators: name: Bouch, Gabriel
Publisher: name: arXiv
Year: 2010
Subjects: subject: Combinatorics (math.CO)
subject: Mathematical Physics (math-ph)
subject: FOS: Mathematics
subject: FOS: Physical sciences

description: Following Richardson and using results of Kesten on First-passage percolation, we obtain an upper bound on the expected perimeter in an Eden Growth Process. Using results of the author from a problem in Statistical Mechanics, we show that the average perimeter of the lattice animals resulting from a very natural family of "growth histories" does not obey a similar bound.
description: 11 pages
Reentrant transition of bosons in a quasiperiodic potential
Creators: name: Cetoli, A.
name: Lundh, E.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Quantum Gases (cond-mat.quant-gas)
subject: FOS: Physical sciences

description: We investigate the behavior of a two dimensional array of Bose-Einstein condensate tubes described by means of a Bose-Hubbard Hamiltonian. Using a Wannier function expansion for the wavefunction in each tube, we compute the Bose-Hubbard parameters related to two different longitudinal potentials, periodic and quasiperiodic. We predict that - upon increasing the external potential strength along the direction of the tubes - the condensate can experience a reentrant transition between a Mott insulating phase and the superfluid one.
description: Accepted for publication in EPL
Magnetic susceptibility of disordered nondiffusive mesoscopic systems
Creators: name: McCann, Edward
name: Richter, Klaus
Publisher: name: Universität Regensburg
Year: 1999
Subjects: subject: 530 Physik

description: Disorder-induced spectral correlations of mesoscopic quantum systems in the nondiffusive regime, and their effect on the magnetic susceptibility, are studied. We perform impurity averaging for nontranslational invariant systems by combining a diagrammatic perturbative approach with semiclassical techniques. This allows us to study the entire range from clean to diffusive systems. As an application we consider the magnetic response of noninteracting electrons in microstructures in the presence of weak disorder. We show that in the ballistic case (an elastic mean free path {\it l} larger than the system size) there exist two distinct regimes of behavior depending on the relative magnitudes of {\it l} and an inelastic scattering length {\it L$_{phi }$} . We present numerical results for square billiards, and derive approximate analytical results for generic chaotic geometries. The magnetic-field dependence and the {\it L$_{phi}$} dependence of the disorder- induced susceptibility are qualitatively similar in both types of geometry.
Creating a new vision for an imagined school : young people from alternative programs explore their experiences with schooling
Creators: name: Panina-Beard, Natalia
Publisher: name: University of British Columbia
Year: 2018

description: Based on Vygotsky’s sociocultural theory, which states that learning and development takes place in the relation between an individual and his or her sociocultural environment, this research focused on the schooling experiences of students attending alternative programs (APs) in British Columbia. Two research questions were addressed: 1) What do the students attending APs say they need to graduate from high school? 2) What would a school look like that provides opportunities for meeting the students’ educational needs and integrating their strengths? Through qualitative methods, eleven students were engaged in a three-phase research process. First, they were interviewed individually. Second, they worked in groups and sharing circles with the support of a researcher, a community Elder and two architects. Third, they created a model for an imagined school that would meet their educational needs and integrate their needs for high school completion. Using thematic analysis, the students reported that mainstream schools did not provide the support and care they needed, did not recognize their teaching and learning needs in a timely manner and did not include their strengths to facilitate school engagement. Conversely, they described the APs as having limited learning opportunities, but providing support and care. Therefore, in their imagined school, they created spaces for: positive relationships with their teachers, rich learning experiences leading to a career, hands-on learning spaces, a garden and a farm. Further, their imagined school was an open and spacious facility connected to the outdoors. The current study contributes to the literature by building from interviews with young people to create with them an imagined school that provides opportunities for both addressing educational needs and building from strengths. Unique to Vygotsky’s theory is a recognition that, along with an experience itself, what matters is the meaning that is made from experience; individuals create meaning in the moment, as well as reinterpret the meaning of experience over time. Through reflection and reinterpretation of experience, the young people in this study were enabled to imagine a school that they had never experienced and, thus, create a school for education.
Dilatancy transition in a granular model
Creators: name: Aristoff, David
name: Radin, Charles
Publisher: name: arXiv
Year: 2010
Subjects: subject: Soft Condensed Matter (cond-mat.soft)
subject: FOS: Physical sciences

description: We introduce a model of granular matter and use a stress ensemble to analyze shearing. Monte Carlo simulation shows the model to exhibit a second order phase transition, associated with the onset of dilatancy.
description: Future versions can be obtained from: http://www.ma.utexas.edu/users/radin/papers/shear2.pdf
Origin of hyperdiffusion in generalized Brownian motion
Creators: name: Siegle, P.
name: Goychuk, I.
name: Hanggi, P.
Publisher: name: arXiv
Year: 2010
Subjects: subject: Statistical Mechanics (cond-mat.stat-mech)
subject: FOS: Physical sciences

description: We study a minimal non-Markovian model of superdiffusion which originates from long-range velocity correlations within the generalized Langevin equation (GLE) approach. The model allows for a three-dimensional Markovian embedding. The emergence of a transient hyperdiffusion, $< Δx^2(t)> \propto t^{2+λ}$, with $λ\sim 1-3$ is detected in tilted washboard potentials before it ends up in a ballistic asymptotic regime. We relate this phenomenon to a transient heating of particles $T_{\rm kin}(t)\propto t^λ$ from the thermal bath temperature $T$ to some maximal kinetic temperature $T_{\rm max}$. This hyperdiffusive transient regime ceases when the particles arrive at the maximal kinetic temperature.
description: Phys. Rev. Lett., in press
Quantum Transport in Nonuniform Magnetic Fields: Aharonov-Bohm Ring as a Spin Switch
Creators: name: Frustaglia, Diego
name: Hentschel, Martina
name: Richter, Klaus
Publisher: name: Universität Regensburg
Year: 2001
Subjects: subject: 530 Physik

description: We study the spin-dependent magneto conductance in mesoscopic rings subject to an inhomogeneous in- plane magnetic field. We show that the polarization direction of transmitted spin- polarized electrons can be controlled via an additional magnetic flux such that spin flips are induced at half a flux quantum. This quantum interference effect is independent of the strength of the nonuniform field applied. We give an analytical explanation for one-dimensional rings and numerical results for corresponding ballistic microstructures.
Non-universal features in the quasi-particle excitation spectra of Andreev billiards and wires
Creators: name: Ihra, Wolfgang
name: Richter, Klaus
Publisher: name: Universität Regensburg
Year: 2001
Subjects: subject: Mesoscopic superconductivity; Hybrid structures; Andreev reflection
subject: 530 Physik

description: We study non-universal features of the quasi- particle excitation spectra of normal-conducting mesoscopic structures, whose classical dynamics are chaotic, and which are coupled to a superconducting lead. In the first part we demonstrate the importance of non-universal contributions in Andreev billiards when the ergodic time of the billiard is of the same order as the mean escape time. Non-universality introduces additional oscillations in the quasi- particle excitation spectrum which are related to the decaying modes of the classical evolution operator in the closed billiard. In the second part we demonstrate that in a long rough wire coupled to a superconductor classical anomalous diffusion modifies the energy scale below which universality holds as a function of the geometrical parameters in comparison to billiards with a narrow superconducting lead.
An island invaded by exotics: a review of freshwater fish in Puerto Rico
Creators: name: Rodríguez-Barreras, Ruber
name: Zapata-Arroyo, Camille
name: L., Wilfredo Falcón
name: De Lourdes Olmeda, María
Publisher: name: Taylor & Francis
Year: 2020
Subjects: subject: Evolutionary Biology
subject: FOS: Biological sciences
subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: Ecology
subject: 69999 Biological Sciences not elsewhere classified
subject: Marine Biology
subject: Inorganic Chemistry
subject: FOS: Chemical sciences

description: The introduction of exotic fishes in streams and water reservoirs has modified autochthonous freshwater fish communities in Puerto Rico. There are approximately 46 fish species in inland waters, and most of them were introduced during the last century. We here summarize relevant information on 46 freshwater fish species reported for the island. Approximately 80% of the species are non-native. An evaluation of the local trade revealed another 128 freshwater fish species are sold locally as pets. This raises serious concerns, as we detected a potential pool of non-native species that are either considered invasive elsewhere, or that, based on their ecology, could become invasive on the island in the near future. We also found that cichlids as a group pose the highest risk to freshwater ecosystems, with 13 species established in the wild, and another 38 potential invaders in the local pet trade. This study may be used as a baseline for the conservation and management purposes of both native and non-native fish species, including the development of strategies for preventing the release of live fish pets into the wild. More specific management for non-native fish, especially those identified here that pose significant threats to Puerto Rico’s native fish and their ecosystems, are warranted.
An optical CMM for flexible on-machine inspection
Creators: name: Buckley, Eric
Publisher: name: University of British Columbia
Year: 2018

description: This thesis presents the design and testing results of an optical coordinate measurement machine for on-machine inspection of machined parts. Inspecting parts on the machine which produces them avoids lost productivity by identifying malfunctioning production machines quickly, thereby reducing the number of out of spec parts produced. The optical coordinate measurement machine designed for this project uses two cameras to track a handheld probe which is used to probe the inspected part. The cameras are designed specifically for the project. They are able to capture target measurements at a very high frequency, which allows averaging of many measurements for increased accuracy. Inspecting parts on-machine requires the system configuration to be flexible, as different machines will need to have the cameras in different locations relative to one another. The cameras are designed to communicate using the flexible EtherCAT fieldbus protocol, and are attached to a modular frame, so that the system can be reconfigured. The probe has four LED targets which are tracked by the cameras and a stylus tip with a probing ball. The reconstruction of the probe tip position requires two stages. First the LED target positions are calculated from the camera measurements using a camera model, and then a geometric fitting is done to match the known probe geometry to the measurements and find the probe tip location. The reconstruction is done by software running in the TwinCAT real-time operating system on a host PC. The calibration of the camera model parameters is done using a CMM with <5um accuracy. The accuracy of the camera calibration is 23.6um at a distance of 1m from the cameras. The probe is calibrated using a procedure developed by the author. The probe ball center calibration accuracy is estimated to be less than 10um. The system is tested by performing a series of measurement tasks probing flat and spherical surfaces. The system shows an accuracy of 30um for these tasks.
Working toward exposure thresholds for blast-induced traumatic brain injury: thoracic and acceleration mechanisms
Creators: name: Courtney, Michael
name: Courtney, Amy
Publisher: name: arXiv
Year: 2011
Subjects: subject: Medical Physics (physics.med-ph)
subject: FOS: Physical sciences

description: Research in blast-induced lung injury resulted in exposure thresholds that are useful in understanding and protecting humans from such injury. Because traumatic brain injury (TBI) due to blast exposure has become a prominent medical and military problem, similar thresholds should be identified that can put available research results in context and guide future research toward protecting warfighters as well as diagnosis and treatment. At least three mechanical mechanisms by which the blast wave may result in brain injury have been proposed - a thoracic mechanism, head acceleration and direct cranial transmission. These mechanisms need not be mutually exclusive. In this study, likely regions of interest for the first two mechanisms based on blast characteristics (positive pulse duration and peak effective overpressure) are developed using available data from blast experiments and related studies, including behind-armor blunt trauma and ballistic pressure wave studies. These related studies are appropriate to include because blast-like pressure waves are produced that result in neurological effects like those caused by blast. Results suggest that injury thresholds for each mechanism are dependent on blast conditions, and that under some conditions, more than one mechanism may contribute. There is a subset of blast conditions likely to result in TBI due to head acceleration and/or a thoracic mechanism without concomitant lung injury. These results can be used to guide experimental designs and compare additional data as they become available. Additional data are needed before actual probabilities or severity of TBI for a given exposure can be described.
description: 11 pages
Theory of Photoemission-type Experiment in the BCS-BEC Crossover Regime of a Superfluid Fermi Gas
Creators: name: Watanabe, Ryota
name: Tsuchiya, Shunji
name: Ohashi, Yoji
Publisher: name: arXiv
Year: 2011
Subjects: subject: Quantum Gases (cond-mat.quant-gas)
subject: FOS: Physical sciences

description: We theoretically investigate the recent photoemission-type experiment on $^{40}$K Fermi gases done by JILA group. Including pairing fluctuations within a strong-coupling $T$-matrix theory, as well as effects of a harmonic trap within the local density approximation, we calculate photoemission spectra in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover region. We show that the energy resolution of the current photoemission experiment is enough to detect the pseudogap phenomenon. We also show how the pseudogap in single-particle excitations continuously changes into the superfluid gap, as one decreases the temperature below the superfluid phase transition temperature. Our results would be useful for the study of single-particle properties of ultracold Fermi gases in the BCS-BEC crossover.
description: 6 pages, 6 figures