3,763 research outputs found
A governance analysis of the Barotse floodplain system, Zambia: identifying obstacles and opportunities
The Barotse floodplain is an ecosystem characterized by a paradox of widespread poverty amidst high ecological and agricultural potential. The CGIAR Research Program on Aquatic Agricultural Systems (AAS) seeks to address this paradox on the assumption that the rural poor have the potential to transform their lives using the aquatic resources in their environment. Understanding the conditions for natural resources use and management is critical for a program that seeks to transform the livelihoods of households dependent on natural resources. The purpose of this report is to identify and analyze key governance variables influencing the livelihood outcomes of AAS program interventions in the Barotse floodplain system
AFM pulling and the folding of donor-acceptor oligorotaxanes: phenomenology and interpretation
The thermodynamic driving force in the self-assembly of the secondary
structure of a class of donor-acceptor oligorotaxanes is elucidated by means of
molecular dynamics simulations of equilibrium isometric single-molecule force
spectroscopy AFM experiments. The oligorotaxanes consist of
cyclobis(paraquat-\emph{p}-phenylene) rings threaded onto an oligomer of
1,5-dioxynaphthalenes linked by polyethers. The simulations are performed in a
high dielectric medium using MM3 as the force field. The resulting force vs.
extension isotherms show a mechanically unstable region in which the molecule
unfolds and, for selected extensions, blinks in the force measurements between
a high-force and a low-force regime. From the force vs. extension data the
molecular potential of mean force is reconstructed using the weighted histogram
analysis method and decomposed into energetic and entropic contributions. The
simulations indicate that the folding of the oligorotaxanes is energetically
favored but entropically penalized, with the energetic contributions overcoming
the entropy penalty and effectively driving the self-assembly. In addition, an
analogy between the single-molecule folding/unfolding events driven by the AFM
tip and the thermodynamic theory of first-order phase transitions is discussed
and general conditions, on the molecule and the cantilever, for the emergence
of mechanical instabilities and blinks in the force measurements in equilibrium
isometric pulling experiments are presented. In particular, it is shown that
the mechanical stability properties observed during the extension are
intimately related to the fluctuations in the force measurements.Comment: 42 pages, 17 figures, accepted to the Journal of Chemical Physic
Chiral molecular films as electron polarizers and polarization modulators
Recent experiments on electron scattering through molecular films have shown
that chiral molecules can be efficient sources of polarized electrons even in
the absence of heavy nuclei as source of a strong spin-orbit interaction. We
show that self-assembled monolayers (SAMs) of chiral molecules are strong
electron polarizers due to the high density effect of the monolayers and
explicitly compute the scattering amplitude off a helical molecular model of
carbon atoms. Longitudinal polarization is shown to be the signature of chiral
scattering. For elastic scattering, we find that at least double scattering
events must take place for longitudinal polarization to arise. We predict
energy windows for strong polarization, determined by the energy dependences of
spin-orbit strength and multiple scattering probability. An incoherent
mechanism for polarization amplification is proposed, that increases the
polarization linearly with the number of helix turns, consistent with recent
experiments on DNA SAMs.Comment: 5 Pages, 4 figure
Inelastic effects in molecular junctions in the Coulomb and Kondo regimes: Nonequilibrium equation-of-motion approach
Inelastic effects in the Coulomb blockade and Kondo regimes of electron
transport through molecular junctions are considered within a simple
nonequilibrium equation-of-motion (EOM) approach. The scheme is
self-consistent, and can qualitatively reproduce the main experimental
observations of vibrational features in Coulomb blockade [H.Park et al., Nature
407, 57 (2000)] and Kondo [L.H.Yu et al., Phys. Rev. Lett. 93, 266802 (2004)]
regimes. Considerations similar to the equilibrium EOM approach by Meir et al.
[Phys. Rev. Lett. 66, 3048 (1991); ibid. 70, 2601 (1993)] are used on the
Keldysh contour to account for the nonequilibrium nature of the junction, and
dressing by appropriate Franck-Condon (FC) factors is used to account for
vibrational features. Results of the equilibrium EOM scheme by Meir et al. are
reproduced in the appropriate limit.Comment: 12 pages, 5 figure
Constructing Diabatic States from Adiabatic States: Extending Generalized Mulliken–Hush to Multiple Charge Centers with Boys Localization
This article shows that, although Boys localization is usually applied to single-electron orbitals, the Boys method itself can be applied to many electron molecular states. For the two-state charge-transfer problem, we show analytically that Boys localization yields the same charge-localized diabatic states as those found by generalized Mulliken–Hush theory. We suggest that for future work in electron transfer, where systems have more than two charge centers, one may benefit by using a variant of Boys localization to construct diabatic potential energy surfaces and extract electronic coupling matrix elements. We discuss two chemical examples of Boys localization and propose a generalization of the Boys algorithm for creating diabatic states with localized spin density that should be useful for Dexter triplet-triplet energy transfer
Molecular transport junctions: Current from electronic excitations in the leads
Using a model comprising a 2-level bridge connecting free electron reservoirs
we show that coupling of a molecular bridge to electron-hole excitations in the
leads can markedly effect the source-drain current through a molecular
junction.In some cases, e.g. molecules that exhibit strong charge transfer
transitions, the contribution from electron-hole excitations can exceed the
Landauer elastic current and dominate the observed conduction.Comment: 4 pages, 2 figures, submitted to PR
Combinations of isoform-targeted histone deacetylase inhibitors and bryostatin analogues display remarkable potency to activate latent HIV without global T-cell activation
AbstractCurrent antiretroviral therapy (ART) for HIV/AIDS slows disease progression by reducing viral loads and increasing CD4 counts. Yet ART is not curative due to the persistence of CD4+ T-cell proviral reservoirs that chronically resupply active virus. Elimination of these reservoirs through the administration of synergistic combinations of latency reversing agents (LRAs), such as histone deacetylase (HDAC) inhibitors and protein kinase C (PKC) modulators, provides a promising strategy to reduce if not eradicate the viral reservoir. Here, we demonstrate that largazole and its analogues are isoform-targeted histone deacetylase inhibitors and potent LRAs. Significantly, these isoform-targeted HDAC inhibitors synergize with PKC modulators, namely bryostatin-1 analogues (bryologs). Implementation of this unprecedented LRA combination induces HIV-1 reactivation to unparalleled levels and avoids global T-cell activation within resting CD4+ T-cells.</jats:p
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