959 research outputs found
Clinicopathological correlation in erythema induratum
Background - Erythema induratum (EI) is a reactive disorder to mycobacterium tuberculosis infection, a diagnosis not to be missed. Erythema nodosum (EN) is the main clinical differential of EI, but a distinctly different pathological condition that can be difficult to distinguish from EI. Methods – In this retrospective review we assess clinical and histological features of 40 EI cases and 16 EN cases. Six experienced dermatologists blindly diagnosed these cases based on clinical images, thereafter the histology was revealed, and they adjusted their diagnoses accordingly. Fleiss Kappa statistics were applied to determine inter-rater variability. A multi-variate logistic regression model determined the clinical and histological features that contribute most to an accurate diagnosis. Results - After assessing the clinical picture 48.8% of the EI cases and 74% of the EN cases were correctly diagnosed. With added histology results 67.1% EI and 81.2% EN cases were correct. EI cases showed inter-rater variability of 0.478 (pvalue < 0.01) before and 0.469 (p-value < 0.01) after histology was revealed. These features combined in a logistic regression model had a higher diagnostic accuracy than the assessors with regard to EI cases. The model was accurate in 100% and 80% of EI and EN cases respectively. Conclusions - While the study was limited by its retrospective nature and small sample size, valuable features (ulceration, vasculitis and lobular or septal panniculitis) were identified. A biopsy of the lower leg markedly increased the diagnostic accuracy, but there was less concordance between assessors, more research is needed to confirm these results
A Noncommutative Sigma Model
We replaced the classical string theory notions of parameter space and
world-time with noncommutative tori and consider maps between these spaces. The
dynamics of mappings between different noncommutative tori were studied and a
noncommutative generalization of the Polyakov action was derived. The quantum
torus was studied in detail as well as *-homomorphisms between different
quantum tori. A finite dimensional representation of the quantum torus was
studied and the partition function and other path integrals were calculated. At
the end we proved existence theorems for mappings between different
noncommutative tori.Comment: The thesis was based on an article by Vargese Mathai and Jonathan
Rosenberg with the same titl
Interplay of Soundcone and Supersonic Propagation in Lattice Models with Power Law Interactions
We study the spreading of correlations and other physical quantities in
quantum lattice models with interactions or hopping decaying like
with the distance . Our focus is on exponents between 0 and 6,
where the interplay of long- and short-range features gives rise to a complex
phenomenology and interesting physical effects, and which is also the relevant
range for experimental realizations with cold atoms, ions, or molecules. We
present analytical and numerical results, providing a comprehensive picture of
spatio-temporal propagation. Lieb-Robinson-type bounds are extended to strongly
long-range interactions where is smaller than the lattice dimension,
and we report particularly sharp bounds that are capable of reproducing regimes
with soundcone as well as supersonic dynamics. Complementary lower bounds prove
that faster-than-soundcone propagation occurs for in any spatial
dimension, although cone-like features are shown to also occur in that regime.
Our results provide guidance for optimizing experimental efforts to harness
long-range interactions in a variety of quantum information and signaling
tasks.Comment: 20 pages, 8 figure
Relaxation timescales and decay of correlations in a long-range interacting quantum simulator
We study the time evolution of correlation functions in long-range
interacting quantum Ising models. For a large class of initial conditions,
exact analytic results are obtained in arbitrary lattice dimension, both for
ferromagnetic and antiferromagnetic coupling, and hence also in the presence of
geometric frustration. In contrast to the nearest-neighbour case, we find that
correlations decay like stretched or compressed exponentials in time. Provided
the long-range character of the interactions is sufficiently strong, pronounced
prethermalization plateaus are observed and relaxation timescales are widely
separated. Specializing to a triangular lattice in two spatial dimensions, we
propose to utilize these results for benchmarking of a recently developed
ion-trap based quantum simulator.Comment: 19 pages, 6 figures; v2: one section removed, appendices added; v3:
upper bound corrected + minor corrections; v4: as publishe
Modelling of trends in Twitter using retweet graph dynamics
In this paper we model user behaviour in Twitter to capture the emergence of
trending topics. For this purpose, we first extensively analyse tweet datasets
of several different events. In particular, for these datasets, we construct
and investigate the retweet graphs. We find that the retweet graph for a
trending topic has a relatively dense largest connected component (LCC). Next,
based on the insights obtained from the analyses of the datasets, we design a
mathematical model that describes the evolution of a retweet graph by three
main parameters. We then quantify, analytically and by simulation, the
influence of the model parameters on the basic characteristics of the retweet
graph, such as the density of edges and the size and density of the LCC.
Finally, we put the model in practice, estimate its parameters and compare the
resulting behavior of the model to our datasets.Comment: 16 pages, 5 figures, presented at WAW 201
A noncommutative sigma model.
We replace the classical string theory notions of mapping
between parameter space and world-time with noncommutative tori mapping between these
spaces. The dynamics of mappings between different noncommutative tori are studied and
noncommutative versions of the Polyakov action and the Euler-Lagrange equations are
derived. The quantum torus is studied in detail, as well as C*-homomorphisms between
different quantum tori. A finite dimensional representation of the quantum torus is studied,
and the partition function and other path integrals are calculated. At the end we prove existence
theorems for mappings between different noncommutative tori.This abstract was presented
at the ‘Studentesimposium
in die Natuurwetenskappe
2011’, presented under
the protection of the Suid-
Afrikaanse Akademie vir
Wetenskap en Kuns. The
symposium was held at the
University of South Africa on
27–28 October 2011.http://www.satnt.ac.zaam201
Investigations on apocynin, a potent NADPH oxidase inhibitor
Polymorphonuclear neutrophils (PMNs) play a major role in inflammatory diseases.
They act as a first line of defense against invading infectious microorganisms. For this purpose,
PMNs contain granules filled with proteolytic and other cytotoxic enzymes. Besides releasing
enzymes, PMNs are also able to phagocytose and to convert oxygen into highly reactive oxygen
species (ROS). Following phagocytosis, ingested microorganisms may be killed inside the
phagosome by a combined action of enzyme activity and ROS production. Although the
formation of ROS by stimulated PMNs is a physiological response which is advantageous to the
host, it can also be detrimental in many inflammatory states in which these radicals give rise to
excessive tissue damage. Therefore, there is an ongoing search for anti-inflammatory compounds
which are able to prevent this damaging ROS production without affecting the other killing
capacities of the PMN.
In 1971, the isolation of apocynin from the roots of Picrorhiza kurroa Royle ex Benth. was
reported. Picrorhiza kurroa is a small, perennial plant growing at high altitudes in the western
Himalayas and which has been used extensively for ages and is still in use in the Ayurvedic
system of medicine in India and Sri Lanka. Following experiments showed that apocynin was a
potent anti-inflammatory agent, based on the selective inhibition of the production of ROS by
activated human PMNs. Although proven to be an active anti-inflammatory compound in several
experimental animal models, the exact mechanism of action of apocynin was still not fully
understood.
In this thesis, experiments are described that have led to a better understanding of the mode of
action by which apocynin inhibits the ROS production by activated human PMNs. One of the
conclusions is that apocynin itself is not active, but that it is converted into an active dimer inside
the phagosomes of activated PMNs
Breakdown of Quasilocality in Long-Range Quantum Lattice Models
We study the nonequilibrium dynamics of correlations in quantum lattice models
in the presence of long-range interactions decaying asymptotically as a power
law. For exponents larger than the lattice dimensionality, a Lieb-Robinson-
type bound effectively restricts the spreading of correlations to a causal
region, but allows supersonic propagation. We show that this decay is not only
sufficient but also necessary. Using tools of quantum metrology, for any
exponents smaller than the lattice dimension, we construct Hamiltonians giving
rise to quantum channels with capacities not restricted to a causal region. An
analytical analysis of long-range Ising models illustrates the disappearance
of the causal region and the creation of correlations becoming distance
independent. Numerical results obtained using matrix product state methods for
the XXZ spin chain reveal the presence of a sound cone for large exponents and
supersonic propagation for small ones. In all models we analyzed, the fast
spreading of correlations follows a power law, but not the exponential
increase of the long-range Lieb-Robinson bound
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