120 research outputs found
Detecting chiral pairing and topological superfluidity using circular dichroism
Realising and probing topological superfluids is a key goal for fundamental
science, with exciting technological promises. Here, we show that chiral
pairing in a two-dimensional topological superfluid can be detected
through circular dichroism, namely, as a difference in the excitation rates
induced by a clockwise and counter-clockwise circular drive. For weak pairing,
this difference is to a very good approximation determined by the Chern number
of the superfluid, whereas there is a non-topological contribution scaling as
the superfluid gap squared that becomes signifiant for stronger pairing. This
gives rise to a competition between the experimentally driven goal to maximise
the critical temperature of the superfluid, and observing a signal given by the
underlying topology. Using a combination of strong coupling Eliashberg and
Berezinskii-Kosterlitz-Thouless theory, we analyse this tension for an atomic
Bose-Fermi gas, which represents a promising platform for realising a chiral
superfluid. We identify a wide range of system parameters where both the
critical temperature is high and the topological contribution to the dichroic
signal is dominant.Comment: 6 pages, 3 figure
Computation of local exchange coefficients in strongly interacting one-dimensional few-body systems: local density approximation and exact results
One-dimensional multi-component Fermi or Bose systems with strong zero-range
interactions can be described in terms of local exchange coefficients and
mapping the problem into a spin model is thus possible. For arbitrary external
confining potentials the local exchanges are given by highly non-trivial
geometric factors that depend solely on the geometry of the confinement through
the single-particle eigenstates of the external potential. To obtain accurate
effective Hamiltonians to describe such systems one needs to be able to compute
these geometric factors with high precision which is difficult due to the
computational complexity of the high-dimensional integrals involved. An
approach using the local density approximation would therefore be a most
welcome approximation due to its simplicity. Here we assess the accuracy of the
local density approximation by going beyond the simple harmonic oscillator that
has been the focus of previous studies and consider some double-wells of
current experimental interest. We find that the local density approximation
works quite well as long as the potentials resemble harmonic wells but break
down for larger barriers. In order to explore the consequences of applying the
local density approximation in a concrete setup we consider quantum state
transfer in the effective spin models that one obtains. Here we find that even
minute deviations in the local exchange coefficients between the exact and the
local density approximation can induce large deviations in the fidelity of
state transfer for four, five, and six particles.Comment: 12 pages, 7 figures, 1 table, final versio
Automatic Verification of Erlang-Style Concurrency
This paper presents an approach to verify safety properties of Erlang-style,
higher-order concurrent programs automatically. Inspired by Core Erlang, we
introduce Lambda-Actor, a prototypical functional language with
pattern-matching algebraic data types, augmented with process creation and
asynchronous message-passing primitives. We formalise an abstract model of
Lambda-Actor programs called Actor Communicating System (ACS) which has a
natural interpretation as a vector addition system, for which some verification
problems are decidable. We give a parametric abstract interpretation framework
for Lambda-Actor and use it to build a polytime computable, flow-based,
abstract semantics of Lambda-Actor programs, which we then use to bootstrap the
ACS construction, thus deriving a more accurate abstract model of the input
program. We have constructed Soter, a tool implementation of the verification
method, thereby obtaining the first fully-automatic, infinite-state model
checker for a core fragment of Erlang. We find that in practice our abstraction
technique is accurate enough to verify an interesting range of safety
properties. Though the ACS coverability problem is Expspace-complete, Soter can
analyse these verification problems surprisingly efficiently.Comment: 12 pages plus appendix, 4 figures, 1 table. The tool is available at
http://mjolnir.cs.ox.ac.uk/soter
An Experimental Evaluation of Deliberate Unsoundness in a Static Program Analyzer
Abstract. Many practical static analyzers are not completely sound by design. Their designers trade soundness in order to increase automa-tion, improve performance, and reduce the number of false positives or the annotation overhead. However, the impact of such design decisions on the effectiveness of an analyzer is not well understood. In this pa-per, we report on the first systematic effort to document and evaluate the sources of unsoundness in a static analyzer. We present a code in-strumentation that reflects the sources of deliberate unsoundness in the.NET static analyzer Clousot. We have instrumented code from several open source projects to evaluate how often concrete executions violate Clousotâs unsound assumptions. In our experiments, this was the case in 8â29 % of all analyzed methods. Our approach and findings can guide users of static analyzers in using them fruitfully, and designers in finding good trade-offs.
Variability-aware Datalog
Variability-aware computing is the efficient application of programs to
different sets of inputs that exhibit some variability. One example is program
analyses applied to Software Product Lines (SPLs). In this paper we present the
design and development of a variability-aware version of the Souffl\'{e}
Datalog engine. The engine can take facts annotated with Presence Conditions
(PCs) as input, and compute the PCs of its inferred facts, eliminating facts
that do not exist in any valid configuration. We evaluate our variability-aware
Souffl\'{e} implementation on several fact sets annotated with PCs to measure
the associated overhead in terms of processing time and database size.Comment: PADL'20 pape
Cognitive behavioural therapy for insomnia in patients with rheumatoid arthritis:protocol for the randomised, single-blinded, parallel-group Sleep-RA trial
Crystal structure of the TLDc domain of oxidation resistance protein 2 from zebrafish
The oxidation resistance proteins (OXR) help to protect eukaryotes from reactive oxygen species. The sole C-terminal domain of the OXR, named TLDc is sufficient to perform this function. However, the mechanism by which oxidation resistance occurs is poorly understood. We present here the crystal structure of the TLDc domain of the oxidation resistance protein 2 from zebrafish. The structure was determined by X-ray crystallography to atomic resolution (0.97Ă
) and adopts an overall globular shape. Two antiparallel β-sheets form a central β-sandwich, surrounded by two helices and two one-turn helices. The fold shares low structural similarity to known structures.Animal science
Developing a digital intervention for cancer survivors: an evidence-, theory- and person-based approach
This paper illustrates a rigorous approach to developing digital interventions using an evidence-, theory- and person-based approach. Intervention planning included a rapid scoping review which identified cancer survivorsâ needs, including barriers and facilitators to intervention success. Review evidence (N=49 papers) informed the interventionâs Guiding Principles, theory-based behavioural analysis and logic model. The intervention was optimised based on feedback on a prototype intervention through interviews (N=96) with cancer survivors and focus groups with NHS staff and cancer charity workers (N=31). Interviews with cancer survivors highlighted barriers to engagement, such as concerns about physical activity worsening fatigue. Focus groups highlighted concerns about support appointment length and how to support distressed participants. Feedback informed intervention modifications, to maximise acceptability, feasibility and likelihood of behaviour change. Our systematic method for understanding user views enabled us to anticipate and address important barriers to engagement. This methodology may be useful to others developing digital interventions
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