608 research outputs found
Supersymmetry and non-Abelian T-duality in type II supergravity
We study the effect of T-duality on supersymmetry in the context of type II
supergravity. For both U(1) Abelian and SU(2) non-Abelian T-duality, we
demonstrate that the supersymmetry variations after T-duality are related to
the variations before T-duality through the Kosmann spinorial Lie derivative,
which vanishes when the Killing spinors are independent of the T-duality
directions. As a byproduct of our analysis, we present closed expressions for
SU(2) T-duality in a class of spacetimes with diagonal Bianchi IX symmetry and
comment on specific examples of T-dual geometries, including a novel AdS3
geometry with large N = (0,4) superconformal symmetry.Comment: 34 pages, v2, wording improved, references updated, v3 references
added, matches published version; v4 signs in section 6 changed to make
consistent with earlier sections, erroneous statement about supersymmetry of
AdS3 S3 S3 S1 non-Abelian T-dual corrected, reference adde
Low frequency radio observations of bi-directional electron beams in the solar corona
The radio signature of a shock travelling through the solar corona is known
as a type II solar radio burst. In rare cases these bursts can exhibit a fine
structure known as `herringbones', which are a direct indicator of particle
acceleration occurring at the shock front. However, few studies have been
performed on herringbones and the details of the underlying particle
acceleration processes are unknown. Here, we use an image processing technique
known as the Hough transform to statistically analyse the herringbone fine
structure in a radio burst at 20-90 MHz observed from the Rosse
Solar-Terrestrial Observatory on 2011 September 22. We identify 188 individual
bursts which are signatures of bi-directional electron beams continuously
accelerated to speeds of 0.16. This occurs at a shock
acceleration site initially at a constant altitude of 0.6 R in
the corona, followed by a shift to 0.5 R. The anti-sunward
beams travel a distance of 170 Mm (and possibly further) away
from the acceleration site, while those travelling toward the sun come to a
stop sooner, reaching a smaller distance of 112 Mm. We show that
the stopping distance for the sunward beams may depend on the total number
density and the velocity of the beam. Our study concludes that a detailed
statistical analysis of herringbone fine structure can provide information on
the physical properties of the corona which lead to these relatively rare radio
bursts
New T-duals with supersymmetry
It is well known that Hopf-fibre T-duality and uplift takes the D1-D5
near-horizon into a class of geometries in 11D where the
internal space is a Calabi-Yau three-fold. Moreover, supersymmetry dictates
that Calabi-Yau is the only permissible -structure manifold.
Generalising this duality chain to non-Abelian isometries, a strong parallel
exists, resulting in the first explicit example of a class of geometries with -structure. Furthermore, the non-Abelian T-dual of
results in a new supersymmetric geometry, which falls outside of all known classifications. We
explore the basic properties of the holographic duals associated to the new
backgrounds. We compute the central charges and show that they are compatible
with a large superconformal algebra in the infra-red.Comment: 30 pages plus one appendix. v2: updated references, v3: published
versio
On Generating Plausible Counterfactual and Semi-Factual Explanations for Deep Learning
There is a growing concern that the recent progress made in AI, especially
regarding the predictive competence of deep learning models, will be undermined
by a failure to properly explain their operation and outputs. In response to
this disquiet counterfactual explanations have become massively popular in
eXplainable AI (XAI) due to their proposed computational psychological, and
legal benefits. In contrast however, semifactuals, which are a similar way
humans commonly explain their reasoning, have surprisingly received no
attention. Most counterfactual methods address tabular rather than image data,
partly due to the nondiscrete nature of the latter making good counterfactuals
difficult to define. Additionally generating plausible looking explanations
which lie on the data manifold is another issue which hampers progress. This
paper advances a novel method for generating plausible counterfactuals (and
semifactuals) for black box CNN classifiers doing computer vision. The present
method, called PlausIble Exceptionality-based Contrastive Explanations (PIECE),
modifies all exceptional features in a test image to be normal from the
perspective of the counterfactual class (hence concretely defining a
counterfactual). Two controlled experiments compare this method to others in
the literature, showing that PIECE not only generates the most plausible
counterfactuals on several measures, but also the best semifactuals.Comment: 4 figures, 9 page
Fitting a square peg into a round hole: are the current Surviving Sepsis Campaign guidelines feasible for Africa?
In their article, Baelani and colleagues surveyed anesthesia providers from African low- and middle-income countries (LMICs) to evaluate whether or not the current Surviving Sepsis Campaign (SSC) guidelines are feasible in such resource-constrained settings. The authors report that an alarmingly low percentage of hospitals have the capacity to implement the SSC guidelines in their entirety but a higher percentage are able to implement the majority of SSC guidelines and grade 1 recommendations. In reality, the probability of adherence to SSC guidelines for septic management is even lower than reported, given that the majority of sepsis management in African LMICs is likely performed by non-intensivists outside of intensive care units. Efforts to address the challenges of managing severely ill patients in LMICs have recently been taken on by the World Health Organization. After reviewing available evidence for sepsis management predominantly from high-income countries, a panel of experts developed a consensus-based strategy tailored for resource-limited settings. However, more research that can evaluate the challenges specific to sepsis management in LMICs and not currently addressed by the SSC guidelines is needed. Comprehensive, evidence-based guidelines combined with innovative approaches to sepsis management in LMICs are required to make a meaningful impact on worldwide sepsis survival
Continuous Transition between Antiferromagnetic Insulator and Paramagnetic Metal in the Pyrochlore Iridate Eu2Ir2O7
Our single crystal study of the magneto-thermal and transport properties of
the pyrochlore iridate Eu2Ir2O7 reveals a continuous phase transition from a
paramagnetic metal to an antiferromagnetic insulator for a sample with
stoichiometry within ~1% resolution. The insulating phase has strong proximity
to an antiferromagnetic semimetal, which is stabilized by several % level of
the off-stoichiometry. Our observations suggest that in addition to electronic
correlation and spin-orbit coupling the magnetic order is essential for opening
the charge gap.Comment: 6 pages, 6 figure
Hypoxia. Regulation of NFκB signalling during inflammation: the role of hydroxylases
NFκB is a master regulator of innate immunity and inflammatory signalling. Microenvironmental hypoxia has long been identified as being coincident with chronic inflammation. The contribution of microenvironmental hypoxia to NFκB-induced inflammation has more recently been appreciated. Identification of the co-regulation of NFκB and hypoxia inducible factor (HIF) pathways by 2-oxo-glutarate-dependent hydroxylase family members has highlighted an intimate relationship between NFκB inflammatory signalling and HIF-mediated hypoxic signalling pathways. Adding another layer of complexity to our understanding of the role of NFκB inflammatory signalling by hypoxia is the recent recognition of the contribution of basal NFκB activity to HIF-1α transcription. This observation implicates an important and previously unappreciated role for NFκB in inflammatory disease where HIF-1α is activated. The present review will discuss recent literature pertaining to the regulation of NFκB inflammatory signalling by hypoxia and some of the inflammatory diseases where this may play an important role. Furthermore, we will discuss the potential for prolylhydroxylase inhibitors in inflammatory disease
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