325 research outputs found
Reform of the United Nations Security Council: equity and efficiency
The United Nations Security Council (UNSC) is critical to global peace and
security, yet more than 20 years of negotiations over its reform have proved fruitless. We
use recent advances in the theory of a priori voting power to present a formal quantitative
appraisal of the implications for democratic equity and efficiency of the “structural
reforms” contained within 11 current reform proposals, as well as the separate effect of
expansion of the UNSC membership. Only one reform proposal–a weakening of the veto
power for Permanent Members by requiring two negative votes for a veto to be effective—
robustly dominates the status quo against our measures of equity and efficiency. Several
proposed structural reforms may actually worsen the issues they ostensibly claim to
resolve
Local Quasitriangular Hopf Algebras
We find a new class of Hopf algebras, local quasitriangular Hopf algebras, which generalize quasitriangular Hopf algebras. Using these Hopf algebras, we obtain solutions of the Yang-Baxter equation in a systematic way. The category of modules with finite cycles over a local quasitriangular Hopf algebra is a braided tensor category
Diffusion-limited reactions and mortal random walkers in confined geometries
Motivated by the diffusion-reaction kinetics on interstellar dust grains, we
study a first-passage problem of mortal random walkers in a confined
two-dimensional geometry. We provide an exact expression for the encounter
probability of two walkers, which is evaluated in limiting cases and checked
against extensive kinetic Monte Carlo simulations. We analyze the continuum
limit which is approached very slowly, with corrections that vanish
logarithmically with the lattice size. We then examine the influence of the
shape of the lattice on the first-passage probability, where we focus on the
aspect ratio dependence: Distorting the lattice always reduces the encounter
probability of two walkers and can exhibit a crossover to the behavior of a
genuinely one-dimensional random walk. The nature of this transition is also
explained qualitatively.Comment: 18 pages, 16 figure
Self-organized criticality in deterministic systems with disorder
Using the Bak-Sneppen model of biological evolution as our paradigm, we
investigate in which cases noise can be substituted with a deterministic signal
without destroying Self-Organized Criticality (SOC). If the deterministic
signal is chaotic the universality class is preserved; some non-universal
features, such as the threshold, depend on the time correlation of the signal.
We also show that, if the signal introduced is periodic, SOC is preserved but
in a different universality class, as long as the spectrum of frequencies is
broad enough.Comment: RevTex, 8 pages, 8 figure
Integrable open boundary conditions for the Bariev model of three coupled XY spin chains
The integrable open-boundary conditions for the Bariev model of three coupled
one-dimensional XY spin chains are studied in the framework of the boundary
quantum inverse scattering method. Three kinds of diagonal boundary K-matrices
leading to nine classes of possible choices of boundary fields are found and
the corresponding integrable boundary terms are presented explicitly. The
boundary Hamiltonian is solved by using the coordinate Bethe ansatz technique
and the Bethe ansatz equations are derived.Comment: 21 pages, no figure
Microlensing as a probe of the Galactic structure; 20 years of microlensing optical depth studies
Microlensing is now a very popular observational astronomical technique. The
investigations accessible through this effect range from the dark matter
problem to the search for extra-solar planets. In this review, the techniques
to search for microlensing effects and to determine optical depths through the
monitoring of large samples of stars will be described. The consequences of the
published results on the knowledge of the Milky-Way structure and its dark
matter component will be discussed. The difficulties and limitations of the
ongoing programs and the perspectives of the microlensing optical depth
technique as a probe of the Galaxy structure will also be detailed.Comment: Accepted for publication in General Relativity and Gravitation.
General Relativity and Gravitation in press (2010) 0
Exact diagonalization of the generalized supersymmetric t-J model with boundaries
We study the generalized supersymmetric model with boundaries in three
different gradings: FFB, BFF and FBF. Starting from the trigonometric R-matrix,
and in the framework of the graded quantum inverse scattering method (QISM), we
solve the eigenvalue problems for the supersymmetric model. A detailed
calculations are presented to obtain the eigenvalues and Bethe ansatz equations
of the supersymmetric model with boundaries in three different
backgrounds.Comment: Latex file, 32 page
The Alaska Arctic Vegetation Archive (AVA-AK)
The Alaska Arctic Vegetation Archive (AVA-AK, GIVD-ID: NA-US-014) is a free, publically available database archive of vegetation-plot data from the Arctic tundra region of northern Alaska. The archive currently contains 24 datasets with 3,026 non-overlapping plots. Of these, 74% have geolocation data with 25-m or better precision. Species cover data and header data are stored in a Turboveg database. A standardized Pan Arctic Species List provides a consistent nomenclature for vascular plants, bryophytes, and lichens in the archive. A web-based online Alaska Arctic Geoecological Atlas (AGA-AK) allows viewing and downloading the species data in a variety of formats, and provides access to a wide variety of ancillary data. We conducted a preliminary cluster analysis of the first 16 datasets (1,613 plots) to examine how the spectrum of derived clusters is related to the suite of datasets, habitat types, and environmental gradients. We present the contents of the archive, assess its strengths and weaknesses, and provide three supplementary files that include the data dictionary, a list of habitat types, an overview of the datasets, and details of the cluster analysis
Constitutive expression and distinct properties of IFN-epsilon protect the female reproductive tract from Zika virus infection
The immunological surveillance factors controlling vulnerability of the female reproductive tract (FRT) to sexually transmitted viral infections are not well understood. Interferon-epsilon (IFNε) is a distinct, immunoregulatory type-I IFN that is constitutively expressed by FRT epithelium and is not induced by pathogens like other antiviral IFNs α, β and λ. We show the necessity of IFNε for Zika Virus (ZIKV) protection by: increased susceptibility of IFNε -/- mice; their “rescue” by intravaginal recombinant IFNε treatment and blockade of protective endogenous IFNε by neutralising antibody. Complementary studies in human FRT cell lines showed IFNε had potent anti-ZIKV activity, associated with transcriptome responses similar to IFNλ but lacking the proinflammatory gene signature of IFNα. IFNε activated STAT1/2 pathways similar to IFNα and λ that were inhibited by ZIKV-encoded non-structural (NS) proteins, but not if IFNε exposure preceded infection. This scenario is provided by the constitutive expression of endogenous IFNε. However, the IFNε expression was not inhibited by ZIKV NS proteins despite their ability to antagonise the expression of IFNβ or λ. Thus, the constitutive expression of IFNε provides cellular resistance to viral strategies of antagonism and maximises the antiviral activity of the FRT. These results show that the unique spatiotemporal properties of IFNε provides an innate immune surveillance network in the FRT that is a significant barrier to viral infection with important implications for prevention and therapy.Rosa C. Coldbeck-Shackley, Ornella Romeo, Sarah Rosli, Linden J. Gearing, Jodee A. Gould, San S. Lim, Kylie H. Van der Hoek, Nicholas S. Eyre, Byron Shue, Sarah A. Robertson, Sonja M. Best, Michelle D. Tate, Paul J. Hertzog, Michael R. Bear
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L-DART: A Penetrator Mission for Lunar Permanently Shadowed Regions
Lunar Direct Analysis of Resource Traps (L‐DART) will address many current knowledge gaps concerning lunar volatiles and permanently shadowed regions (PSRs), providing in-situ ground truth data to calibrate numerous existing remote datasets. It builds on UK expertise in developing and testing penetrator system concepts for the Moon and Europa (e.g. MOONLITE). Following release of a Penetrator Descent Module in lunar orbit (Figure 1), its Penetrator Delivery System performs de-orbit and orientation before releasing the instrumented Penetrator to penetrate a few meters into target lunar surface at ~300 m/s. The penetrator itself serves as the sampling tool and an on-board mass spectrometer analyses in-situ the volatiles released both in the impact and in the subsequent thermal soak from lander to surrounding regolith. A pair of 3‐axis accelerometers measure regolith structure during the landing event and constrain penetrator final location. Temperature sensors enable regolith thermal properties to be deduced. Pre-and post impact imagery is obtained for context. Science is complete and data relayed to Earth within 1-2 hours, minimizing system mass and lifetime requirements. Possible landing sites include Cabeus (for comparison with LCROSS) or Shoemaker which exhibits excess hydrogen, or areas indicated by LRO to exhibit putative surface frost. Alternatively, L‐DART could target the hypothesised ancient (paleo) south pole and hence potentially ancient volatiles
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