Operational K-theory

We study the operational bivariant theory associated to the covariant theory of Grothendieck groups of coherent sheaves, and prove that it has many geometric properties analogous to those of operational Chow theory. This operational K-theory agrees with Grothendieck groups of vector bundles on smooth varieties, admits a natural map from the Grothendieck group of perfect complexes on general varieties, satisfies descent for Chow envelopes, and is A^1-homotopy invariant. Furthermore, we show that the operational K-theory of a complete linear variety is dual to the Grothendieck group of coherent sheaves. As an application, we show that the K-theory of perfect complexes on any complete toric threefold surjects onto this group. Finally, we identify the equivariant operational K-theory of an arbitrary toric variety with the ring of integral piecewise exponential functions on the associated fan.Comment: 38 pages; v2: new exampes in Sections 5 and 7, and an new application (Theorem 1.4), showing that the natural map from K-theory of perfect complexes to the dual of the Grothendieck group of coherent sheaves is surjective for complete toric threefolds; v3: final version published in Documenta Mat

Darren McGarvey (2022) The Social Distance Between Us. London: Ebury Press, hardback, 400 pp., ISBN 9781529104080

Darren McGarvey’s latest book The Social Distance Between Us: How Remote Politics Wrecked Britain explores the idea that ‘proximity dictates how we identify and relate to society and the problems it faces - ultimately dictating how, and whether, we strive to resolve them’. Darren does this exploration in a book consisting of an introduction, two acts with an interlude between them and then a coda

Racial Disparities in College Students’ Scholastic Adjustment Amidst COVID-19: The Protective Function of Campus Resources and Supports

Scientific investigations are needed to understand the extent to which COVID-19 has affected, and exacerbated racial disparities in, college students’ scholastic adjustment. We propose a study based on two waves of data collected as part of a large-scale, longitudinal study on college students’ well-being amidst COVID-19. More specifically, we will evaluate a model of risk and protective factors for college students’ scholastic adjustment across three time points within the 2020-21 academic year. The first aim is to evaluate contextual risk factors for college students’ scholastic difficulties during COVID-19 and whether contextual risk is more pronounced for minoritized students. The second aim is to examine whether campus supports and resources buffer risk for scholastic difficulties for all students, and especially minoritized students, during COVID-19. College students (N=522) from two, residential liberal arts colleges participated in the first wave of data in the fall and will be invited to participate in two waves of data collection in the spring. Developmental researchers conduct large-scale longitudinal studies in collaborative teams because such studies are extremely labor- and time-intensive. Examples of tasks that necessitate teamwork include recruiting and compensating participants; managing data; and conducting analyses. See below for details about methods and analyse

Veils and Cloaks of Ignorance: Under-used Tools for Conflict Resolution

Published in cooperation with the American Bar Association Section of Dispute Resolutio

Darren McGarvey, (2017) Poverty Safari: Understanding the anger of Britain’s Underclass

In Poverty Safari: Understanding the Anger of Britain’s Underclass Darren McGarvey (aka Loki) sets out to give voice to the feelings, concerns and anger of people from deprived communities all around Britain. McGarvey uses the book to explore his current truths, refreshingly not by attempting to present definitive answers, but instead by offering observations and understandings based on his own experiences with what feels like an invitation to explore and discuss what he airs. An immense power of the book for me is in McGarvey naming and articulating a long rumbling sense of things not being as polar as they are regularly presented; where a desire to make the complex simple often means our human messiness goes unacknowledged, with packaged ‘solutions’ based on a particular ideological viewpoint touted as the answer before question framing is ever adequately considered.  This polar thinking is compounded by people’s truths so often going unarticulated due to the weighted assumptions of deemed experts being prioritised and/or for fear or experience of folk being ‘unheard’, ‘ridiculed’ or having perceived or real negative consequences for themselves, communities or organisations they might be associated with

Superfluid Helium Tanker (SFHT) study

Replenishment of superfluid helium (SFHe) offers the potential of extending the on-orbit life of observatories, satellite instruments, sensors and laboratories which operate in the 2 K temperature regime. A reference set of resupply customers was identified as representing realistic helium servicing requirements and interfaces for the first 10 years of superfluid helium tanker (SFHT) operations. These included the Space Infrared Telescope Facility (SIRTF), the Advanced X-ray Astrophysics Facility (AXAF), the Particle Astrophysics Magnet Facility (Astromag), and the Microgravity and Materials Processing Sciences Facility (MMPS)/Critical Point Phenomena Facility (CPPF). A mixed-fleet approach to SFHT utilization was considered. The tanker permits servicing from the Shuttle cargo bay, in situ when attached to the OMV and carried to the user spacecraft, and as a depot at the Space Station. A SFHT Dewar ground servicing concept was developed which uses a dedicated ground cooling heat exchanger to convert all the liquid, after initial fill as normal fluid, to superfluid for launch. This concept permits the tanker to be filled to a near full condition, and then cooled without any loss of fluid. The final load condition can be saturated superfluid with any desired ullage volume, or the tank can be totally filed and pressurized. The SFHT Dewar and helium plumbing system design has sufficient component redundancy to meet fail-operational, fail-safe requirements, and is designed structurally to meet a 50 mission life usage requirement. Technology development recommendations were made for the selected SFHT concept, and a Program Plan and cost estimate prepared for a phase C/D program spanning 72 months from initiation through first launch in 1997

A Graphene-based Hot Electron Transistor

We experimentally demonstrate DC functionality of graphene-based hot electron transistors, which we call Graphene Base Transistors (GBT). The fabrication scheme is potentially compatible with silicon technology and can be carried out at the wafer scale with standard silicon technology. The state of the GBTs can be switched by a potential applied to the transistor base, which is made of graphene. Transfer characteristics of the GBTs show ON/OFF current ratios exceeding 50.000.Comment: 18 pages, 6 figure