K-orbit closures and Barbasch-Evens-Magyar varieties

We define the Barbasch-Evens-Magyar variety. We show it is isomorphic to the smooth variety defined in [D. Barbasch-S. Evens '94] that maps finite-to-one to a symmetric orbit closure, thereby giving a resolution of singularities in certain cases. Our definition parallels [P. Magyar '98]'s construction of the Bott-Samelson variety [H. C. Hansen '73, M. Demazure '74]. From this alternative viewpoint, one deduces a graphical description in type A, stratification into closed subvarieties of the same kind, and determination of the torus-fixed points. Moreover, we explain how these manifolds inherit a natural symplectic structure with Hamiltonian torus action. We then prove that the moment polytope is expressed in terms of the moment polytope of a Bott-Samelson variety.Comment: 26 pages, 4 figure

The Geography of Incarceration

The Boston Foundation's Boston Indicators Project, MassINC, and the Massachusetts Criminal Justice Reform Coalition, released The Geography of Incarceration: The Cost and Consequences of High Incarceration Rates in Vulnerable City Neighborhoods, a new study that compares the geography of incarceration to the geography of crime in our city.The report accessed a novel data set from Suffolk County Sheriff Steve Tompkins and depicts how incarcerations have had a disproportionate impact on Boston's most vulnerable neighborhoods."This is needed work because the American criminal justice is characterized by high incarceration rates, especially for people of color. This produces cascading negative effects, not just on the lives of the imprisoned but on their families, neighborhoods and our city as a whole," said Paul Grogan, President and CEO of the Foundation.  "I'm hopeful that this work will build on the leadership Chief Justice Gants and the commitment from Governor Baker, Speaker DeLeo and Senate President Rosenberg to work with the Council of State Governments to produce meaningful reform."Among the report's findings, are:Even as Massachusetts has touted its "progressiveness," incarceration rates have been rising faster in recent years in this state than in the rest of the United States, as a whole.More was spent in 2013 incarcerating Codman Square residents than on statewide gang prevention efforts.The cost of housing all Suffolk County Jail inmates in 2013 was two-and-a-half times the Commonwealth's combined FY13 budgets for Bunker Hill and Roxbury community colleges and nearly as much as Boston's combined budgets for Parks and Recreation and Youth and Families departments.The report was released during a forum at The Boston Foundation that included a panel discussion with Suffolk County Sheriff Steve Tompkins, Boston City Councilor Andrea Campbell, State Representative Evandro Carvalho, and John Larivee, President & CEO of Community Resources for Justice. The report recommended a series of reforms, including the redesigning houses of correction so they excel at addressing risks and needs, and eliminating mandatory minimum jail sentences, and in increased focus on diversion and re-entry programming for offenders

The role of endosymbionts in the evolution of haploid-male genetic systems in scale insects (Coccoidea)

There is an extraordinary diversity in genetic systems across species, but this variation remains poorly understood. In part, this is because the mechanisms responsible for transitions between systems are often unknown. A recent hypothesis has suggested that conflict between hosts and endosymbiotic microorganisms over transmission could drive the transition from diplodiploidy to systems with male haploidy (haplodiploidy, including arrhenotoky and paternal genome elimination [PGE]). Here, we present the first formal test of this idea with a comparative analysis across scale insects (Hemiptera: Coccoidea). Scale insects are renowned for their large variation in genetic systems, and multiple transitions between diplodiploidy and haplodiploidy have taken place within this group. Additionally, most species rely on endosymbiotic microorganisms to provide them with essential nutrients lacking in their diet. We show that species harboring endosymbionts are indeed more likely to have a genetic system with male haploidy, which supports the hypothesis that endosymbionts might have played a role in the transition to haplodiploidy. We also extend our analysis to consider the relationship between endosymbiont presence and transitions to parthenogenesis. Although in scale insects there is no such overall association, species harboring eukaryote endosymbionts were more likely to be parthenogenetic than those with bacterial symbionts. These results support the idea that intergenomic conflict can drive the evolution of novel genetic systems and affect host reproduction.Peer reviewe

Reionization in Technicolor

We present the Technicolor Dawn simulations, a suite of cosmological radiation-hydrodynamic simulations of the first 1.2 billion years. By modeling a spatially-inhomogeneous UVB on-the-fly with 24 frequencies and resolving dark matter halos down to $10^8 M_\odot$ within 12 $h^{-1}$ Mpc volumes, our simulations unify observations of the intergalactic and circumgalactic media, galaxies, and reionization into a common framework. The only empirically-tuned parameter, the fraction $f_{\mathrm{esc,gal}}(z)$ of ionizing photons that escape the interstellar medium, is adjusted to match observations of the Lyman-$\alpha$ forest and the cosmic microwave background. With this single calibration, our simulations reproduce the history of reionization; the stellar mass-star formation rate relation of galaxies; the number density and metallicity of damped Lyman-$\alpha$ absorbers (DLAs) at $z\sim5$; the abundance of weak metal absorbers; the ultraviolet background (UVB) amplitude; and the Lyman-$\alpha$ flux power spectrum at $z=5.4$. The galaxy stellar mass and UV luminosity functions are underproduced by $\leq2\times$, suggesting an overly vigorous feedback model. The mean transmission in the Lyman-$\alpha$ forest is underproduced at $z<6$, indicating tension between measurements of the UVB amplitude and Lyman-$\alpha$ transmission. The observed SiIV column density distribution is reasonably well-reproduced ($\sim 1\sigma$ low). By contrast, CIV remains significantly underproduced despite being boosted by an intense $>4$ Ryd UVB. Solving this problem by increasing metal yields would overproduce both weak absorbers and DLA metallicities. Instead, the observed strength of high-ionization emission from high-redshift galaxies and absorption from their environments suggest that the ionizing flux from conventional stellar population models is too soft.Comment: 24 pages, 17 figures, accepted to MNRA

Using think-aloud interviews to characterize model-based reasoning in electronics for a laboratory course assessment

Models of physical systems are used to explain and predict experimental results and observations. The Modeling Framework for Experimental Physics describes the process by which physicists revise their models to account for the newly acquired observations, or change their apparatus to better represent their models when they encounter discrepancies between actual and expected behavior of a system. While modeling is a nationally recognized learning outcome for undergraduate physics lab courses, no assessments of students' model-based reasoning exist for upper-division labs. As part of a larger effort to create two assessments of students' modeling abilities, we used the Modeling Framework to develop and code think-aloud problem-solving activities centered on investigating an inverting amplifier circuit. This study is the second phase of a multiphase assessment instrument development process. Here, we focus on characterizing the range of modeling pathways students employ while interpreting the output signal of a circuit functioning far outside its recommended operation range. We end by discussing four outcomes of this work: (1) Students engaged in all modeling subtasks, and they spent the most time making measurements, making comparisons, and enacting revisions; (2) Each subtask occurred in close temporal proximity to all over subtasks; (3) Sometimes, students propose causes that do not follow logically from observed discrepancies; (4) Similarly, students often rely on their experiential knowledge and enact revisions that do not follow logically from articulated proposed causes.Comment: 18 pages, 5 figure

A Family Affair: Library Opportunities to Connect With Parents and Families

Parents are important aspects of our students’ academic lives, and as such, should be acknowledged and considered as allies and potential partners with libraries. This article presents ideas for many ways in which libraries can engage with parents and families, while also exploring the benefits of such efforts. The broad areas in which these efforts fall include 1) overall student success, 2) connecting with other student-supporting and student-reaching entities on campus, and 3) supporting the critical efforts of student recruitment and retention. In this article, examples of different parent engagement opportunities are also discussed, including involvement in campus events, engaging with parent associations, considerations of legacy engagement, and collaboration with other campus units. The results of these parent-library initiatives and connections can help accomplish a variety of things including supporting student academic success, ensuring that the library is involved in other university student outreach efforts, contributing to development and fundraising activities and finally, supporting the recruitment and retention of students

Characterizing lab instructors' self-reported learning goals to inform development of an experimental modeling skills assessment

The ability to develop, use, and refine models of experimental systems is a nationally recognized learning outcome for undergraduate physics lab courses. However, no assessments of students' model-based reasoning exist for upper-division labs. This study is the first step toward development of modeling assessments for optics and electronics labs. In order to identify test objectives that are likely relevant across many institutional contexts, we interviewed 35 lab instructors about the ways they incorporate modeling in their course learning goals and activities. The study design was informed by the Modeling Framework for Experimental Physics. This framework conceptualizes modeling as consisting of multiple subtasks: making measurements, constructing system models, comparing data to predictions, proposing causes for discrepancies, and enacting revisions to models or apparatus. We found that each modeling subtask was identified by multiple instructors as an important learning outcome for their course. Based on these results, we argue that test objectives should include probing students' competence with most modeling subtasks, and test items should be designed to elicit students' justifications for choosing particular modeling pathways. In addition to discussing these and other implications for assessment, we also identify future areas of research related to the role of modeling in optics and electronics labs.Comment: 24 pages, 2 figures, 5 tables; submitted to Phys. Rev. PE

Changes in the near edge X-ray absorption fine structure of hybrid organic-inorganic resists upon exposure

We report on the near edge X-ray absorption fine structure (NEXAFS) spectroscopy of hybrid organic-inorganic resists. These materials are nonchemically amplified systems based on Si, Zr, and Ti oxides, synthesized from organically modified precursors and transition metal alkoxides by a sol-gel route and designed for ultraviolet, extreme ultraviolet and electron beam lithography. The experiments were conducted using a scanning transmission X-ray microscope (STXM) which combines high spatial-resolution microscopy and NEXAFS spectroscopy. The absorption spectra were collected in the proximity of the carbon edge (~ 290 eV) before and after in situ exposure, enabling the measurement of a significant photo-induced degradation of the organic group (phenyl or methyl methacrylate, respectively), the degree of which depends on the configuration of the ligand. Photo-induced degradation was more efficient in the resist synthesized with pendant phenyl substituents than it was in the case of systems based on bridging phenyl groups. The degradation of the methyl methacrylate group was relatively efficient, with about half of the initial ligands dissociated upon exposure. Our data reveal that the such dissociation can produce different outcomes, depending on the structural configuration. While all the organic groups were expected to detach and desorb from the resist in their entirety, a sizeable amount of them remain and form undesired byproducts such as alkene chains. In the framework of the materials synthesis and engineering through specific building blocks, these results provide a deeper insight into the photochemistry of resists, in particular for extreme ultraviolet lithography

Top-philic Vector-Like Portal to Scalar Dark Matter

We investigate the phenomenology of scalar singlet dark matter candidates that couple dominantly to the Standard Model via a Yukawa interaction with the top quark and a colored vector-like fermion. We estimate the viability of this vector-like portal scenario with respect to the most recent bounds from dark matter direct and indirect detection, as well as to dark matter and vector-like mediator searches at colliders. Moreover, we take QCD radiative corrections into account in all our theoretical calculations. This work complements analyses related both to models featuring a scalar singlet coupled through a vector-like portal to light quarks, and to scenarios in which the dark matter is a Majorana singlet coupled to the Standard Model through scalar colored particles (akin to simplified models inspired by supersymmetry). Our study puts especially forward the complementarity of different search strategies from different contexts, and we show that current experiments allow for testing dark matter masses ranging up to 700 GeV and mediator masses ranging up to 6 TeV.Comment: 15 pages, 11 figures; version accepted by PR