Stereocontrolled enantioselective total synthesis of the [2+2] quadrigemine alkaloids.

A unified strategy for enantioselective total synthesis of all stereoisomers of the 2+2 family of quadrigemine alkaloids is reported. In this approach, two enantioselective intramolecular Heck reactions are carried out at the same time on precursors fashioned in four steps from either meso- or (+)-chimonanthine to form the two critical quaternary carbons of the peripheral cyclotryptamine rings of these products. Useful levels of catalyst control are realized in either desymmetrizing a meso precursor or controlling diastereoselectivity in elaborating C2-symmetic intermediates. None of the synthetic quadrigemines are identical with alkaloids isolated previously and referred to as quadrigemines A and E. In addition, we report improvements in our previous total syntheses of (+)- or (-)-quadrigemine C that shortened the synthetic sequence to 10 steps and provided these products in 2.2% overall yield from tryptamine

Exploring Privilege in the Digital Divide:Implications for Theory, Policy, and Practice

Background and Objectives: The digital revolution has resulted in innovative solutions and technologies that can support the well-being, independence, and health of seniors. Yet, the notion of the “digital divide” presents significant inequities in terms of who accesses and benefits from the digital landscape. To better understand the social and structural inequities of the digital divide, a realist synthesis was conducted to: inform theoretical understandings of information and communication technologies (ICTs); understand the practicalities of access and use inequities; uncover practices that facilitate digital literacy and participation; and recommend policies to mitigate the digital divide.Research Design and Methods : A systematic search yielded 55 articles published between 2006 and 2016. Synthesis of existing knowledge, combined with user-experience elicited through a deliberative dialogue session with community stakeholders (n=35), made visible a pattern of privilege that determined individual agency in ICT access and use.Results: Though age is consistently centralized as the key determinant of the digital divide, our analyses, which encompassed both van Dijk’s resources and appropriation theory and intersectionality, appraised this notion and revealed that age is not the sole determinant. Findings highlight the role of other factors that contribute to digital inequity among community-dwelling middle-aged (45-64) and older (65+) adults, including education, income, gender, and generational status.Discussion and Implications: Informed by results of a realist synthesis that was guided by intersectional perspectives, a conceptual framework was developed outlining implications for theory, policy, and practice to address the wicked problem that is the digital divide

Helfrich-Canham bending energy as a constrained non-linear sigma model

The Helfrich-Canham bending energy is identified with a non-linear sigma model for a unit vector. The identification, however, is dependent on one additional constraint: that the unit vector be constrained to lie orthogonal to the surface. The presence of this constraint adds a source to the divergence of the stress tensor for this vector so that it is not conserved. The stress tensor which is conserved is identified and its conservation shown to reproduce the correct shape equation.Comment: 5 page

Range corrections for two-neutron halo nuclei in effective theory

The range corrections to the universal properties and structure of two-neutron halo nuclei are investigated within an effective quantum mechanics framework. Treating the nucleus as an effective three-body system, we make a systematic improvement upon previous calculations by calculating the linear range corrections at next-to-leading order. Since the effective ranges for the neutron-core interactions are not known, we estimate the effective range to be set by the inverse of the pion mass. We investigate the possibility of excited Efimov states in two-neutron halo nuclei and calculate their mean square radii to next-to-leading order. We find that the effective range corrections are generally small and the leading order predictions are very robust.Comment: 19 pages, 4 eps figures, revtex4, final version to appear in Nucl. Phys.

Fission of a multiphase membrane tube

A common mechanism for intracellular transport is the use of controlled deformations of the membrane to create spherical or tubular buds. While the basic physical properties of homogeneous membranes are relatively well-known, the effects of inhomogeneities within membranes are very much an active field of study. Membrane domains enriched in certain lipids in particular are attracting much attention, and in this Letter we investigate the effect of such domains on the shape and fate of membrane tubes. Recent experiments have demonstrated that forced lipid phase separation can trigger tube fission, and we demonstrate how this can be understood purely from the difference in elastic constants between the domains. Moreover, the proposed model predicts timescales for fission that agree well with experimental findings

Porous silicon formation and electropolishing

Electrochemical etching of silicon in hydrofluoride containing electrolytes leads to pore formation for low and to electropolishing for high applied current. The transition between pore formation and polishing is accompanied by a change of the valence of the electrochemical dissolution reaction. The local etching rate at the interface between the semiconductor and the electrolyte is determined by the local current density. We model the transport of reactants and reaction products and thus the current density in both, the semiconductor and the electrolyte. Basic features of the chemical reaction at the interface are summarized in law of mass action type boundary conditions for the transport equations at the interface. We investigate the linear stability of a planar and flat interface. Upon increasing the current density the stability flips either through a change of the valence of the dissolution reaction or by a nonlinear boundary conditions at the interface.Comment: 18 pages, 8 figure

Membrane geometry with auxiliary variables and quadratic constraints

Consider a surface described by a Hamiltonian which depends only on the metric and extrinsic curvature induced on the surface. The metric and the curvature, along with the basis vectors which connect them to the embedding functions defining the surface, are introduced as auxiliary variables by adding appropriate constraints, all of them quadratic. The response of the Hamiltonian to a deformation in each of the variables is examined and the relationship between the multipliers implementing the constraints and the conserved stress tensor of the theory established.Comment: 8 page

Contextual factors for aging well:Creating socially engaging spaces through the use of deliberative dialogues

Purpose of the Study: Home and community engagement are key contextual factors for aging well, particularly for older adults in vulnerable social positions. A community-based participatory action research project conducted in Western Canada examined how to best use the shared amenity spaces in a low-income seniors' apartment complex in order to connect services and programs with tenants and to provide opportunities for service providers and local stakeholders to build upon and create new relationships toward collaboration and service delivery. Design and Methods: Pre-move deliberative dialogue workshops (n = 4) were conducted with stakeholders (e.g., service providers, developers, and municipal government employees). Workshop participants (n = 24) generated ideas and plans on how physical and social environments can contribute to the social engagement of senior tenants. Results: Shared dialogue led to community investment and asset sharing by integrating the knowledge and experiences of multiple stakeholder groups into the planning process. This article highlights how collaborative planning approaches for the effective use of the social environment (e.g., social programming), within the physical environment (e.g., amenity and community spaces), can generate rich and illuminating data for informing enhancements in the social environment of apartment dwelling low-income seniors. Contextual challenges to service provision are discussed, including the need for communication about and coordination of on-site programming, culturally diverse and responsive programming, and longterm funding. Implications: Prolonging independent community living with the assistance of support services should be a goal to both delay premature relocation into institutional care and meet the preferences of older adults.</p

Phase ordering and shape deformation of two-phase membranes

Within a coupled-field Ginzburg-Landau model we study analytically phase separation and accompanying shape deformation on a two-phase elastic membrane in simple geometries such as cylinders, spheres and tori. Using an exact periodic domain wall solution we solve for the shape and phase ordering field, and estimate the degree of deformation of the membrane. The results are pertinent to a preferential phase separation in regions of differing curvature on a variety of vesicles.Comment: 4 pages, submitted to PR