Democracy Counts 2020: Record-Breaking Turnout and Student Resiliency

This report contains findings from the National Study of Learning, Voting, and Engagement (NSLVE, pronounced n-solve), a landmark study of U.S. college and university student voting. Launched in 2013, NSLVE consists of a database of more than 10 million de-identified student records that have been combined with publicly available voting records for each of the 2012, 2014, 2016, 2018, and now, 2020 elections. Participating institutions include two- and four-year public and private colleges and universities, including graduate programs. Campuses must opt in, and at the time of this report, roughly 1,200 colleges and universities from all 50 states and the District of Columbia participate. For this report, we examine 1,051 campuses representing approximately 9 million student voters

Reconciling optical and radio observations of the binary millisecond pulsar PSR J1640+2224

Previous optical and radio observations of the binary millisecond pulsar PSR J1640+2224 have come to inconsistent conclusions about the identity of its companion, with some observations suggesting the companion is a low-mass helium-core (He-core) white dwarf (WD), while others indicate it is most likely a high-mass carbon-oxygen (CO) WD. Binary evolution models predict PSR J1640+2224 most likely formed in a low-mass X-ray binary (LMXB) based on the pulsar's short spin period and long-period, low-eccentricity orbit, in which case its companion should be a He-core WD with mass about $0.35 - 0.39 \, M_\odot$, depending on metallicity. If it is instead a CO WD, that would suggest the system has an unusual formation history. In this paper we present the first astrometric parallax measurement for this system from observations made with the Very Long Baseline Array (VLBA), from which we determine the distance to be $1520^{+170}_{-150}\,\mathrm{pc}$. We use this distance and a reanalysis of archival optical observations originally taken in 1995 with the Wide Field Planetary Camera 2 (WFPC2) on the Hubble Space Telescope (HST) in order to measure the WD's mass. We also incorporate improvements in calibration, extinction model, and WD cooling models. We find that the existing observations are not sufficient to tightly constrain the companion mass, but we conclude the WD mass is $>0.4\,M_\odot$ with $>90\%$ confidence. The limiting factor in our analysis is the low signal-to-noise ratio of the original HST observations.Comment: 6 pages, 5 figure

Mechanistic investigations of DNA reactive carcinogens at low dose, through analysis of DNA adducts, mutations and DNA repair.

Genetic toxicology assesses the genotoxic potential of chemicals in consumer products, pharmaceuticals and from agricultural and industrial processes. Such assessment is integral in hazard identification and risk assessment to prevent unnecessary human exposure and limit cancer risk. Human risk assessments for genotoxic alkylating agents were based upon linear dose-response models where genotoxicity accrues proportionally with dose. Evidence is accumulating to support a non-linear dose-response at low doses of ethyl methanesulfonate (EMS), a model alkylating agent. For acceptance of non-linear dose responses, a strong explanatory mechanism of action needs to be elucidated. In the following work, low dose mutagenic effects of methyl nitorosurea (MNU), the most potent alkylating agent, have been examined in AHH-1 human lymphoblastoid cells using the HPRT assay. An increase in mutant frequency was not observed until 0.01pg/ml MNU (LOGEL, Lowest Observed Genotoxic Effect Level) with a No-Observed Genotoxic Effect Level (NOGEL) at 0.0075pg/ml MNU. Of interest, is the apparent hormesis induced at 0.0025pg/ml MNU. The principle adduct responsible for MNU mutagenesis is 0 6Methylguanine (06MeG) that miscodes during replication and becomes fixed as GC->AT transitions. Accordingly, the non-linear increase in mutant frequency is accompanied by a non-linear increase in GC->AT transitions. Furthermore, evidence is provided that implicates methlyguanine methyltransferase (MGMT) in protecting DNA from MNU induced mutagenesis by repairing 0 6MeG at low doses, thereby creating the NOGEL. AHH-1 cells treated with 0 6Benzylguanine (06BG), to inactivate MGMT, were hypersensitive to low dose MNU mutagenesis. At 0.0075pg/ml MNU, there was a three-fold increase in mutant frequency and an increase in proportion of GC-^AT transitions, from 28% to 48% in MGMT inactivated cells. This thesis presents a non-linear dose-response for MNU with a strong biological mechanism of action involving DNA repair

Structural basis of mitochondrial receptor binding and constriction by DRP1.

Mitochondrial inheritance, genome maintenance and metabolic adaptation depend on organelle fission by dynamin-related protein 1 (DRP1) and its mitochondrial receptors. DRP1 receptors include the paralogues mitochondrial dynamics proteins of 49 and 51 kDa (MID49 and MID51) and mitochondrial fission factor (MFF); however, the mechanisms by which these proteins recruit and regulate DRP1 are unknown. Here we present a cryo-electron microscopy structure of full-length human DRP1 co-assembled with MID49 and an analysis of structure- and disease-based mutations. We report that GTP induces a marked elongation and rotation of the GTPase domain, bundle-signalling element and connecting hinge loops of DRP1. In this conformation, a network of multivalent interactions promotes the polymerization of a linear DRP1 filament with MID49 or MID51. After co-assembly, GTP hydrolysis and exchange lead to MID receptor dissociation, filament shortening and curling of DRP1 oligomers into constricted and closed rings. Together, these views of full-length, receptor- and nucleotide-bound conformations reveal how DRP1 performs mechanical work through nucleotide-driven allostery

Complete reducibility and subgroups of exceptional algebraic groups

This survey article has two components. The first part gives a gentle introduction to Serre's notion of $G$-complete reducibility, where $G$ is a connected reductive algebraic group defined over an algebraically closed field. The second part concerns consequences of this theory when $G$ is simple of exceptional type, specifically its role in elucidating the subgroup structure of $G$. The latter subject has a history going back about sixty years. We give an overview of what is known, up to the present day. We also take the opportunity to offer several corrections to the literature.Comment: 42 page

Radiation-Pressure-Mediated Control of an Optomechanical Cavity

We describe and demonstrate a method to control a detuned movable-mirror Fabry-Perot cavity using radiation pressure in the presence of a strong optical spring. At frequencies below the optical spring resonance, self-locking of the cavity is achieved intrinsically by the optomechanical (OM) interaction between the cavity field and the movable end mirror. The OM interaction results in a high rigidity and reduced susceptibility of the mirror to external forces. However, due to a finite delay time in the cavity, this enhanced rigidity is accompanied by an anti-damping force, which destabilizes the cavity. The cavity is stabilized by applying external feedback in a frequency band around the optical spring resonance. The error signal is sensed in the amplitude quadrature of the transmitted beam with a photodetector. An amplitude modulator in the input path to the cavity modulates the light intensity to provide the stabilizing radiation pressure force

Nod1 signaling overcomes resistance of S. pneumoniae to opsonophagocytic killing

Airway infection by the Gram-positive pathogen Streptococcus pneumoniae (Sp) leads to recruitment of neutrophils but limited bacterial killing by these cells. Co-colonization by Sp and a Gram-negative species, Haemophilus influenzae (Hi), provides sufficient stimulus to induce neutrophil and complement-mediated clearance of Sp from the mucosal surface in a murine model. Products from Hi, but not Sp, also promote killing of Sp by ex vivo neutrophil-enriched peritoneal exudate cells. Here we identify the stimulus from Hi as its peptidoglycan. Enhancement of opsonophagocytic killing was facilitated by signaling through nucleotide-binding oligomerization domain-1 (Nod1), which is involved in recognition of γ-D-glutamyl-meso-diaminopimelic acid (meso-DAP) contained in cell walls of Hi but not Sp. Neutrophils from mice treated with Hi or compounds containing meso-DAP, including synthetic peptidoglycan fragments, showed increased Sp killing in a Nod1-dependent manner. Moreover, Nod1-/- mice showed reduced Hi-induced clearance of Sp during co-colonization. These observations offer insight into mechanisms of microbial competition and demonstrate the importance of Nod1 in neutrophil-mediated clearance of bacteria in vivo