4,752 research outputs found
Moduli spaces of torsion sheaves on K3 surfaces and derived equivalences
We show that for many moduli spaces M of torsion sheaves on K3 surfaces S,
the functor D(S) -> D(M) induced by the universal sheaf is a P-functor, hence
can be used to construct an autoequivalence of D(M), and that this
autoequivalence can be factored into geometrically meaningful equivalences
associated to abelian fibrations and Mukai flops. Along the way we produce a
derived equivalence between two compact hyperkaehler 2g-folds that are not
birational, for every g >= 2. We also speculate about an approach to showing
that birational moduli spaces of sheaves on K3 surfaces are derived-equivalent.Comment: 28 pages. typos corrected. final version to appear in JLM
Gendered landscapes of safety : how women construct and navigate the urban landscape to avoid sexual violence.
This article presents findings from an online survey gathering quantitative and qualitative data from men and women students at a university in the north of England in 2016. The survey explored their perceptions of safety and experiences of interpersonal violence during their time as a student, both on and off campus. We show how women were more likely to report sexual violence compared to men. We also show how women students, compared to men, were less likely to say they never felt unsafe as they moved away from the university into the city, and as they moved from day into night. We illustrate how interconnecting factors construct womenâs perceptions of safety, and subsequently, how locations perceived as unsafe âhotspotsâ, become physical barriers impeding womenâs access to public and educational spaces. Consequently, we outline measures to enhance womenâs safety whilst at university
Drivers in solar deployment in India: A state-level analysis
This report considers the drivers of inter-state solar power deployment in India, and what mix of policies are most appropriate to help India reach its ambitious solar power target
Convective activity in a Martian magma chamber recorded by P-zoning in Tissint olivine
The Tissint Martian meteorite is an unusual depleted olivineâphyric shergottite, reportedly sourced from a mantleâderived melt within a deep magma chamber. Here, we report major and trace element data for Tissint olivine and pyroxene, and use these data to provide new insights into the dynamics of the Tissint magma chamber. The presence of irregularly spaced oscillatory phosphorous (P)ârich bands in olivine, along with geochemical evidence indicative of a closed magmatic system, implies that the olivine grains were subject to solute trapping caused by vigorous crystal convection within the Tissint magma chamber. Calculated equilibration temperatures for the earliest crystallizing (antecrystic) olivine cores suggest a Tissint magma source temperature of 1680 °C, and a local Martian mantle temperature of 1560 °C during the late Amazonianâthe latter being consistent with the ambient mantle temperature of Archean Earth
Beyond mystery: Putting algorithmic accountability in context
Critical algorithm scholarship has demonstrated the difficulties of attributing accountability for the actions and effects of algorithmic systems. In this commentary, we argue that we cannot stop at denouncing the lack of accountability for algorithms and their effects but must engage the broader systems and distributed agencies that algorithmic systems exist within; including standards, regulations, technologies, and social relations. To this end, we explore accountability in âthe Generated Detective,â an algorithmically generated comic. Taking up the mantle of detectives ourselves, we investigate accountability in relation to this piece of experimental fiction. We problematize efforts to effect accountability through transparency by undertaking a simple operation: asking for permission to re-publish a set of the algorithmically selected and modified words and images which make the frames of the comic. Recounting this process, we demonstrate slippage between the âcomplicationâ of the algorithm and the obscurity of the legal and institutional structures in which it exists
The Nature of Heavy Quasiparticles in Magnetically Ordered Heavy Fermions
The optical conductivity of the heavy fermions UPd2Al3 and UPt3 has been
measured in the frequency range from 10 GHz to 1.2 THz (0.04 meV to 5 meV) at
temperatures 1 K < T < 300 K. In both compounds a well pronounced pseudogap of
less than a meV develops in the optical response at low temperatures; we relate
this to the antiferromagnetic ordering. From the energy dependence of the
effective electronic mass and scattering rate we derive the energies essential
for the heavy quasiparticle. We find that the enhancement of the mass mainly
occurs below the energy which is related to magnetic correlations between the
local magnetic moments and the itinerant electrons. This implies that the
magnetic order in these compounds is the pre-requisite to the formation of the
heavy quasiparticle and eventually of superconductivity.Comment: RevTeX, 4 pages, 3 figures, email:
[email protected]
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