Abelian varieties with isogenous reductions

If A and B are abelian varieties over a number field K such that there are non-trivial geometric homomorphisms of abelian varieties between reductions of A and B at most primes of K, then there exists a non-trivial (geometric) homomorphism from A to B defined over an algebraic closure of K.Comment: Final version, with French abstract; to appear in Comptes Rendus - S\'erie Math\'ematiqu

Governance Struggles and Policy Processes in Disaster Risk Reduction: A Case Study from Nepal

In the neo-liberal climate of reduced responsibility for the state, alongside global platforms established to implement the Hyogo Framework for Action, a new arena opens for a multitude of stakeholders to engage in disaster risk reduction (DRR). The key role that the state can play in instituting effective DRR tends to receive little attention, yet in situations where the state apparatus is weak, such as in Nepal, it becomes evident that integrating DRR into development is a particularly challenging task. Due to the political situation in Nepal, progress has been stalled in providing a legislative context conducive to effective DRR. This paper traces the evolution of key DRR initiatives that have been developed in spite of the challenging governance context, such as the National Strategy for Disaster Risk Management and the Nepal Risk Reduction Consortium. Informed by in-depth interviews with key informants, the argument is made that the dedicated efforts of national and international non-governmental organisations, multilateral agencies and donors in mainstreaming DRR demonstrate that considerable progress can be made even where government departments are protective of their own interests and are slow to enact policies to support DRR. The paper suggests however, that without stronger engagement of key political actors the prospects for further progress in DRR may be limited. The findings have implications for other post-conflict countries or weak states engaging in DRR

Stepwise Photoinduced Electron Transfer in a Tetrathiafulvalene-Phenothiazine-Ruthenium Triad

A molecular triad comprising a [Ru(bpy)3]2+ (bpy = 2,2′‐bipyridine) photosensitizer, a primary phenothiazine (PTZ) donor and a secondary (extended) tetrathiafulvalene (exTTF) donor was synthesized and explored by UV/Vis transient absorption spectroscopy. Initial photoinduced electron transfer from PTZ to the 3MLCT‐excited [Ru(bpy)3]2+ occurs within less than 60 ps, and subsequently PTZ is regenerated by electron transfer from exTTF with a time constant of 300 ps. The resulting photoproduct comprising exTTF·+ and [Ru(bpy)3]+ has a lifetime of 6100 ps in de‐aerated CH3CN at room temperature. Additional one‐ and two‐pulse laser flash photolysis studies of the triad were performed in the presence of excess methyl viologen (MV2+), to explore the possibility of light‐driven charge accumulation on exTTF. MV2+ clearly oxidized [Ru(bpy)3]+ and thereby re‐instated ground‐state [Ru(bpy)3]2+ in triads in which exTTF had been oxidized to exTTF·+, but further excitation of the solution containing the exTTF·+‐PTZ‐[Ru(bpy)3]2+ photoproduct did not provide evidence for exTTF2+. Nevertheless, it seems that the design principle of a covalent donor‐donor‐sensitizer triad (as opposed to simpler donor‐sensitizer dyads) is beneficial for light‐driven accumulation of oxidation equivalents. These investigations are relevant in the greater context of multi‐electron photoredox chemistry and artificial photosynthesis

Surveying the Inner Halo of the Galaxy with 2MASS-Selected Horizontal Branch Candidates

We use 2MASS photometry to select blue horizontal branch (BHB) candidates covering the sky |b|>15 deg. A 12.5<J<15.5 sample of BHB stars traces the thick disk and inner halo to d<9 kpc, with a density comparable to that of M giant stars. We base our sample selection strategy on the Century Survey Galactic Halo Project, a survey that provides a complete, spectroscopically-identified sample of blue stars to a similar depth as the 2MASS catalog. We show that a -0.20<(J-H)_0<0.10, -0.10<(H-K)_0<0.10 color-selected sample of stars is 65% complete for BHB stars, and is composed of 47% BHB stars. We apply this photometric selection to the full 2MASS catalog, and see no spatial overdensities of BHB candidates at high Galactic latitude |b|>50 deg. We insert simulated star streams into the data and conclude that the high Galactic latitude BHB candidates are consistent with having no ~5 deg wide star stream with density greater than 0.33 objects deg^-2 at the 95% confidence level. The absence of structure suggests there have been no major accretion events in the inner halo in the last few Gyr. However, at low Galactic latitudes a two-point angular correlation analysis reveals structure on angular scales <1 deg. This structure is apparently associated with stars in the thick disk, and has a physical scale of 10-100 pc. Interestingly, such structures are expected by cosmological simulations that predict the majority of the thick disk may arise from accretion and disruption of satellite mergers.Comment: 11 pages, including figures. Accepted by AJ with minor revision

Abelian varieties with isogenous reductions

Let $A_1$ and $A_2$ be abelian varieties over a number field $K$. We prove that if there exists a non-trivial morphism of abelian varieties between reductions of $A_1$ and $A_2$ at a sufficiently high percentage of primes, then there exists a non-trivial morphism $A_1\rightarrow A_2$ over $\bar{K}$. Along the way, we give an upper bound for the number of components of a reductive subgroup of $\mathrm{GL}_n$ whose intersection with the union of $\mathbb{Q}$-rational conjugacy classes of $\mathrm{GL}_n$ is Zariski-dense. This can be regarded as a generalization of the Minkowski–Schur theorem on faithful representations of finite groups with rational characters

Improving Usability of Social and Behavioral Sciences’ Evidence: A Call to Action for a National Infrastructure Project for Mining Our Knowledge

Over the last century, the social and behavioral sciences have accumulated a vast storehouse of knowledge with the potential to transform society and all its constituents. Unfortunately, this knowledge has accumulated in a form (e.g., journal papers) and scale that makes it extremely difficult to search, categorize, analyze, and integrate across studies. In this commentary based on a National Science Foundation-funded workshop, we describe the social and behavioral sciences’ knowledge-management problem. We discuss the knowledge-scale problem and how we lack a common language, a common format to represent knowledge, a means to analyze and summarize in an automated way, and approaches to visualize knowledge at a large scale. We then describe that we need a collaborative research program between information systems, information science, and computer science (IICS) researchers and social and behavioral science (SBS) researchers to develop information system artifacts to address the problem that many scientific disciplines share but that the social and behavioral sciences have uniquely not addressed

Design of Experiments Analysis of Crosslink Density and Plasticizer Effects on Rheological Properties of Guanidine-based Covalent Adaptable Networks

We report the use of a design of experiments (DOE) analysis to study the effects of varying crosslink density and plasticizer loading on the thermorheological properties of guanidine-based covalent adaptable networks (CANs). CANs engage in dynamic bond-exchange reactions above the glass transition, resulting in shifts between thermoset-like materials and states capable of flow that can be greatly impacted by network characteristics beyond the exchange reaction itself. The synthesis of guanidine-based CANs by combination of carbodiimide-containing oligomers and various ratios of amine-containing crosslinker molecules and phthalate plasticizer was used to create a library of CANs with varying crosslink density and equal concentrations of guanidine functionalities. Additionally, glass transition was tuned by modifying plasticizer loading. CANs at three degrees of crosslink density and two degrees of plasticizer loading were characterized by rheometry and dynamic mechanical analysis. The resulting data were analyzed using linear regression and two-factor analysis of variance (ANOVA), which provided statistically significant evidence that relaxation times and activation energies varied directly with crosslink density but exhibited little change due to plasticizer content

Chemical and Physical Tailoring of Guanidine-based Covalent Adaptable Networks

We present the synthesis of two different guanidine-based CAN materials which, unlike traditional thermoset polymer networks, can undergo an exchange reaction called thermal guanidine metathesis (TGM) and be reprocessed. Thermosets, which are polymer networks characterized by permanent covalent crosslinks between chains, have a myriad of commercial applications. However, a major drawback to thermosets is their inability to be reprocessed. To develop a more sustainable thermoset-like material, CANs exhibit breaking and reforming of crosslinks under certain conditions that enable reprocessing. To elucidate the effects of varied guanidine structure on the rheological and mechanical properties of these dissociative CANs, we synthesized two guanidine-based CANs via reaction of a carbodiimide-containing polymer with two bifunctional amines. We found that the CAN with a more sterically congested guanidine was able to relax stress more quickly than the less sterically hindered CAN, supporting the influence of steric bulkiness on the kinetic and thermodynamic properties of the TGM reaction in guanidine-based CANs