arXiv subjects

David Webb

Publications and source records attributed to David Webb.

16 recordsLinked to original sources

arXiv2026

Grades, equity and graduation rates: a quantitative analysis of the association of learning assistants with improved student outcomes

In this paper we use multilevel modeling of 10 introductory courses from four STEM disciplines to quantify associations of Learning Assistants (LAs) with the student-level outcomes, pass-rates, and retention. Overall we find that having an LA in a class is associated with improvement of these metrics for all students. Fur- thermore, along with all students showing improvement, we find noticeable demographic differences in the amount of improvement. For instance, LAs seem to be associated with larger improvements in pass-rates for historically marginalized groups, and larger increases in graduation rates for women identifying as belonging to historically marginalized races and ethnicities when compared to students from the same group but with class sections without LAs. This indicates that Learning Assistant programs may be an excellent investment for diverse institutions.

physics.ed-ph↗

arXiv2025

Polarization Diagnostics Applied to Coronal Mass Ejections and the Background Solar Wind

The ratio of radially to tangentially polarized Thomson-scattered white light provides a powerful tool for locating the 3D position of compact structures in the solar corona and inner heliosphere, and the Polarimeter to Unify the Corona and Heliosphere (PUNCH) has been designed to take full advantage of this diagnostic capability. Interestingly, this same observable that establishes the position of transient blob-like structures becomes a local measure of the slope of the global falloff of density in the background solar wind. It is thus important to characterize the extent along the line of sight of structures being studied, in order to determine whether they are sufficiently compact for 3D positioning. In this paper, we build from analyses of individual lines of sight to three-dimensional models of coronal mass ejections (CMEs), allowing us to consider how accurately polarization properties of the transient and quiescent solar wind are diagnosed. In this way, we demonstrate the challenges and opportunities presented by PUNCH polarization data for various quantitative diagnostics.

astro-ph.SR↗

arXiv2023

Natural language processing on customer note data

Automatic analysis of customer data for businesses is an area that is of interest to companies. Business to business data is studied rarely in academia due to the sensitive nature of such information. Applying natural language processing can speed up the analysis of prohibitively large sets of data. This paper addresses this subject and applies sentiment analysis, topic modelling and keyword extraction to a B2B data set. We show that accurate sentiment can be extracted from the notes automatically and the notes can be sorted by relevance into different topics. We see that without clear separation topics can lack relevance to a business context.

cs.CL↗

arXiv2021

Starshade Rendezvous: Exoplanet Sensitivity and Observing Strategy

Launching a starshade to rendezvous with the Nancy Grace Roman Space Telescope would provide the first opportunity to directly image the habitable zones of nearby sunlike stars in the coming decade. A report on the science and feasibility of such a mission was recently submitted to NASA as a probe study concept. The driving objective of the concept is to determine whether Earth-like exoplanets exist in the habitable zones of the nearest sunlike stars and have biosignature gases in their atmospheres. With the sensitivity provided by this telescope, it is possible to measure the brightness of zodiacal dust disks around the nearest sunlike stars and establish how their population compares to our own. In addition, known gas-giant exoplanets can be targeted to measure their atmospheric metallicity and thereby determine if the correlation with planet mass follows the trend observed in the Solar System and hinted at by exoplanet transit spectroscopy data. In this paper we provide the details of the calculations used to estimate the sensitivity of Roman with a starshade and describe the publicly available Python-based source code used to make these calculations. Given the fixed capability of Roman and the constrained observing windows inherent for the starshade, we calculate the sensitivity of the combined observatory to detect these three types of targets and we present an overall observing strategy that enables us to achieve these objectives.

astro-ph.IM↗

arXiv2020

Earth-affecting Solar Transients: A Review of Progresses in Solar Cycle 24

This review article summarizes the advancement in the studies of Earth-affecting solar transients in the last decade that encompasses most of solar cycle 24. The Sun Earth is an integrated physical system in which the space environment of the Earth sustains continuous influence from mass, magnetic field and radiation energy output of the Sun in varying time scales from minutes to millennium. This article addresses short time scale events, from minutes to days that directly cause transient disturbances in the Earth space environment and generate intense adverse effects on advanced technological systems of human society. Such transient events largely fall into the following four types: (1) solar flares, (2) coronal mass ejections (CMEs) including their interplanetary counterparts ICMEs, (3) solar energetic particle (SEP) events, and (4) stream interaction regions (SIRs) including corotating interaction regions (CIRs). In the last decade, the unprecedented multi viewpoint observations of the Sun from space, enabled by STEREO Ahead/Behind spacecraft in combination with a suite of observatories along the Sun-Earth lines, have provided much more accurate and global measurements of the size, speed, propagation direction and morphology of CMEs in both 3-D and over a large volume in the heliosphere. Several advanced MHD models have been developed to simulate realistic CME events from the initiation on the Sun until their arrival at 1 AU. Much progress has been made on detailed kinematic and dynamic behaviors of CMEs, including non-radial motion, rotation and deformation of CMEs, CME-CME interaction, and stealth CMEs and problematic ICMEs. The knowledge about SEPs has also been significantly improved.

astro-ph.SR↗

arXiv2019

Historical astronomical data: urgent need for preservation, digitization enabling scientific exploration

Over the past decades and even centuries, the astronomical community has accumulated a signif-icant heritage of recorded observations of a great many astronomical objects. Those records con-tain irreplaceable information about long-term evolutionary and non-evolutionary changes in our Universe, and their preservation and digitization is vital. Unfortunately, most of those data risk becoming degraded and thence totally lost. We hereby call upon the astronomical community and US funding agencies to recognize the gravity of the situation, and to commit to an interna-tional preservation and digitization efforts through comprehensive long-term planning supported by adequate resources, prioritizing where the expected scientific gains, vulnerability of the origi-nals and availability of relevant infrastructure so dictates. The importance and urgency of this issue has been recognized recently by General Assembly XXX of the International Astronomical Union (IAU) in its Resolution B3: "on preservation, digitization and scientific exploration of his-torical astronomical data". We outline the rationale of this promotion, provide examples of new science through successful recovery efforts, and review the potential losses to science if nothing it done.

astro-ph.IM↗

arXiv2018

The Habitable Exoplanet Observatory (HabEx) Mission Concept Study Interim Report

For the first time in human history, technologies have matured sufficiently to enable a mission capable of discovering and characterizing habitable planets like Earth orbiting sunlike stars other than the Sun. At the same time, such a platform would enable unique science not possible from ground-based facilities. This science is broad and exciting, ranging from new investigations of our own solar system to a full range of astrophysics disciplines. The Habitable Exoplanet Observatory, or HabEx, is one of four studies currently being undertaken by NASA in preparation for the 2020 Astrophysics Decadal Survey. HabEx has been designed to be the Great Observatory of the 2030s, with community involvement through a competed and funded Guest Observer (GO) program. This interim report describes the HabEx baseline concept, which is a space-based 4-meter diameter telescope mission concept with ultraviolet (UV), optical, and near-infrared (near-IR) imaging and spectroscopy capabilities. More information on HabEx can be found at https://www.jpl.nasa.gov/habex

astro-ph.IM↗

arXiv2018

Hierarchical Linear Modeling Approach to Measuring the Effects of Class Size and Other Classroom Characteristics on Student Learning in an Active-Learning Based Introductory Physics Course

The effect of class size on student learning has numerous policy implications and has been a major subject of conversation and research for decades. Despite this, few studies have been done on class size in the context of university settings or physics courses. After discussing some of the reasoning behind hierarchical linear modeling (HLM) as well as how to interpret the results of an HLM analysis while grounding this study in measurement theory as it applies to course grades, this paper goes on to examine the effect of class size in active-learning based introductory physics courses using a series of hierarchical linear models. It is found that class size over the ranges studied does not have a significant effect on student grades which were used as a proxy for student understanding of the underlying material. However, a variety of issues and limitations means this is certainly not the end of the story and there is still much to be done and discussed when it comes to these courses and the various factors which affect student achievement in them, both theoretically and empirically.

physics.ed-ph↗

arXiv2018

Robin and Steklov isospectral manifolds

We use two of the most fruitful methods for constructing isospectral manifolds, the Sunada method and the torus action method, to construct manifolds whose Dirichlet-to-Neumann operators are isospectral at all frequencies. The manifolds are also isospectral for the Robin boundary value problem for all choices of Robin parameter. As in the sloshing problem, we can also impose mixed Dirichlet-Neumann conditions on parts of the boundary. Among the examples we exhibit are Steklov isospectral flat surfaces with boundary, planar domains with isospectral sloshing problems, and Steklov isospectral metrics on balls of any dimension greater than 5. In particular, the latter are the first examples of Steklov isospectral manifolds of dimension greater than 2 that have connected boundaries.

math.DG↗

arXiv2018

Beyond sunspots: Studies using the McIntosh Archive of global solar magnetic field patterns

In 1964 (Solar Cycle 20; SC 20), Patrick McIntosh began creating hand-drawn synoptic maps of solar magnetic features, based on H$\alpha$ images. These synoptic maps were unique in that they traced magnetic polarity inversion lines, and connected widely separated filaments, fibril patterns, and plage corridors to reveal the large-scale organization of the solar magnetic field. Coronal hole boundaries were later added to the maps, which were produced, more or less continuously, into 2009 (i.e., the start of SC 24). The result was a record of $\sim45$ years ($\sim570$ Carrington rotations), or nearly four complete solar cycles of synoptic maps. We are currently scanning, digitizing and archiving these maps, with the final, searchable versions publicly available at NOAA's National Centers for Environmental Information. In this paper we present preliminary scientific studies using the archived maps from SC 23. We show the global evolution of closed magnetic structures (e.g., sunspots, plage, and filaments) in relation to open magnetic structures (e.g., coronal holes), and examine how both relate to the shifting patterns of large-scale positive and negative polarity regions.

astro-ph.SR↗

arXiv2018

Transplantation and isogeny of intermediate Jacobians of compact K\"ahler manifolds

We give a general method for constructing compact K\"ahler manifolds $X_1$ and $X_2$ whose intermediate Jacobians $J^k(X_1)$ and $J^k(X_2)$ are isogenous for each $k$, and we exhibit some examples. The method is based upon the algebraic transplantation formalism arising from Sunada's technique for constructing pairs of compact Riemannian manifolds whose Laplace spectra are the same. We also show that the method produces compact Riemannian manifolds whose Lazzeri Jacobians are isogenous.

math.AG↗

arXiv2017

A generalized Stoner criterion and versatile spin ordering in two-dimensional spin-orbit coupled electron systems

Spin-orbit coupling is a single-particle phenomenon known to generate topological order, and electron-electron interactions cause ordered many-body phases to exist. The rich interplay of these two mechanisms is present in a broad range of materials, and has been the subject of considerable ongoing research and controversy. Here we demonstrate that interacting two-dimensional electron systems with strong spin-orbit coupling exhibit a variety of time reversal symmetry breaking phases with unconventional spin alignment. We first prove that a Stoner-type criterion can be formulated for the spin polarization response to an electric field, which predicts that the spin polarization susceptibility diverges at a certain value of the electron-electron interaction strength. The divergence indicates the possibility of unconventional ferromagnetic phases even in the absence of any applied electric or magnetic field. This leads us, in the second part of this work, to study interacting Rashba spin-orbit coupled semiconductors in equilibrium in the Hartree-Fock approximation as a generic minimal model. Using classical Monte-Carlo simulations we construct the complete phase diagram of the system as a function of density and spin-orbit coupling strength. It includes both an out-of-plane spin polarized phase and in-plane spin-polarized phases with shifted Fermi surfaces and rich spin textures, reminiscent of the Pomeranchuk instability, as well as two different Fermi-liquid phases having one and two Fermi surfaces, respectively, which are separated by a Lifshitz transition. We discuss possibilities for experimental observation and useful application of these novel phases, especially in the context of electric-field-controlled macroscopic spin polarizations.

cond-mat.mes-hall↗

arXiv2012

Variation of Instructor-Student Interactions in an Introductory Interactive Physics Course

The physics instruction at UC Davis for life science majors takes place in a long-standing reformed large-enrollment physics course in which the discussion/lab instructors (primarily graduate student teaching assistants) implement the interactive-engagement (IE) elements of the course. Because so many different instructors participate in disseminating the IE course elements, we find it essential to the instructors professional development to observe and document the student-instructor interactions within the classroom. Out of this effort, we have developed a computerized real-time instructor observation tool (RIOT) to take data of student-instructor interactions. We use the RIOT to observe 29 different instructors for five hours each over the course of one quarter, for a total of about 150 hours of class time, finding that the range of instructor behaviors is more extreme than previously assumed. In this paper, we introduce the RIOT and describe how the variation present across 29 different instructors can provide students in the same course with significantly different course experiences.

physics.ed-ph↗

arXiv2012

Sixteen years of Collaborative Learning through Active Sense-making in Physics (CLASP) at UC Davis

This paper describes our large reformed introductory physics course at UC Davis, which bioscience students have been taking since 1996. The central feature of this course is a focus on sense-making by the students during the five hours per week discussion/labs in which the students take part in activities emphasizing peer-peer discussions, argumentation, and presentations of ideas. The course differs in many fundamental ways from traditionally taught introductory physics courses. After discussing the unique features of CLASP and its implementation at UC Davis, various student outcome measures are presented showing increased performance by students who took the CLASP course compared to students who took a traditionally taught introductory physics course. Measures we use include upper-division GPAs, MCAT scores, FCI gains, and MPEX-II scores.

physics.ed-ph↗

arXiv2011

Classical Equivalence and Quantum Equivalence of Magnetic Fields on Flat Tori

Let M be a real 2m-torus equipped with a translation-invariant metric h and a translation-invariant symplectic form w; the latter we interpret as a magnetic field on M. The Hamiltonian flow of half the norm-squared function induced by h on T^*M (the "kinetic energy") with respect to the twisted symplectic form w_{T^*M}+ \pi^*w describes the trajectories of a particle moving on M under the influence of the magnetic field w. If [w] is an integral cohomology class, then we can study the geometric quantization of the symplectic manifold (T^*M,w_{T^*M}+\pi^*w) with the kinetic energy Hamiltonian. We say that the quantizations of two such tori (M_1,h_1,w_1) and (M_2,h_2,w_2) are quantum equivalent if their quantum spectra, i.e., the spectra of the associated quantum Hamiltonian operators, coincide; these quantum Hamiltonian operators are proportional to the h_j-induced bundle Laplacians on powers of the Hermitian line bundle on M with Chern class [w]. In this paper, we construct continuous families {(M,h_t)}_t of mutually nonisospectral flat tori (M,h_t), each endowed with a translation-invariant symplectic structure w, such that the associated classical Hamiltonian systems are pairwise equivalent. If w represents an integer cohomology class, then the (M,h_t,w) also have the same quantum spectra. We show moreover that for any translation-invariant metric h and any translation-invariant symplectic structure w on M that represents an integer cohomology class, the associated quantum spectrum determines whether (M,h,w) is Kaehler, and that all translation-invariant Kaehler structures (h,w) of given volume on M have the same quantum spectra. Finally, we construct pairs of magnetic fields (M,h,w_1), (M,h,w_2) having the same quantum spectra but nonsymplectomorphic classical phase spaces. In some of these examples the pairs consist of Kaehler manifolds.

math.DG↗

arXiv2010

Quantum Equivalent Magnetic Fields that Are Not Classically Equivalent

We construct pairs of compact K\"ahler-Einstein manifolds $(M_i,g_i,\omega_i)$ ($i=1,2)$ of complex dimension $n$ with the following properties: The canonical line bundle $L_i=\bigwedge^n T^*M_i$ has Chern class $[\omega_i/2\pi]$, and for each integer $k$ the tensor powers $L_1^{\otimes k}$ and $L_2^{\otimes k}$ are isospectral for the bundle Laplacian associated with the canonical connection, while $M_1$ and $M_2$ -- and hence $T^*M_1$ and $T^*M_2$ -- are not homeomorphic. In the context of geometric quantization, we interpret these examples as magnetic fields which are quantum equivalent but not classically equivalent. Moreover, we construct many examples of line bundles $L$, pairs of potentials $Q_1$, $Q_2$ on the base manifold, and pairs of connections $\nabla_1$, $\nabla_2$ on $L$ such that for each integer $k$ the associated Schr\"odinger operators on $L^{\otimes k}$ are isospectral.

math.DG↗