101 research outputs found
Seasonal and recurrent intensive care unit admissions for acute severe asthma in children
Life-threatening attacks of asthma requiring intensive care unit (ICU) management at Red Cross War Memorial Children's Hospital in Cape Town were noted to occur in some patients in the same or adjacent months of different years. A retrospective case-controlled study was performed of 21 such 'seasonal' patients who presented to the ICU over a 14-year period. The group tnade up 6,5% of all asthma patients adtnitted to the ICU and their 65 admissions made up 15,6% of all ICU asthma admissions during this period. The control group consisted of patients with recurrent admissions that occurred in 'random' months. The two groups were compared in respect of demographic and clinical data. Patients requiring seasonal adtnissions were shown to form a distinct sub-population of children with severe asthma, some with a family history of fatal asthma, who were less likely to 'outgrow' asthma in childhood, were Inore likely to require Inaintenance steroid therapy for asthtna management, and significantly more often had positive radioallergosorbent tests to Aspergillus and Cladosporium sp. and to grass pollen. A retrospective analysis of dates of severe asthtna attacks Inay identify individual seasonality, which is a risk factor for life-threatening and intractable asthma
A covariant approach to general field space metric in multi-field inflation
We present a covariant formalism for general multi-field system which enables
us to obtain higher order action of cosmological perturbations easily and
systematically. The effects of the field space geometry, described by the
Riemann curvature tensor of the field space, are naturally incorporated. We
explicitly calculate up to the cubic order action which is necessary to
estimate non-Gaussianity and present those geometric terms which have not yet
known before.Comment: (v1) 18 pages, 1 figure; (v2) references added, typos corrected, to
appear in Journal of Cosmology and Astroparticle Physics; (v3) typos in (54),
(62) and (64) correcte
Quantum measurement problem and cluster separability
A modified Beltrametti-Cassinelli-Lahti model of measurement apparatus that
satisfies both the probability reproducibility condition and the
objectification requirement is constructed. Only measurements on microsystems
are considered. The cluster separability forms a basis for the first working
hypothesis: the current version of quantum mechanics leaves open what happens
to systems when they change their separation status. New rules that close this
gap can therefore be added without disturbing the logic of quantum mechanics.
The second working hypothesis is that registration apparatuses for microsystems
must contain detectors and that their readings are signals from detectors. This
implies that separation status of a microsystem changes during both preparation
and registration. A new rule that specifies what happens at these changes and
that guarantees the objectification is formulated and discussed. A part of our
result has certain similarity with 'collapse of the wave function'.Comment: 31 pages, no figure. Published versio
Two- and Three-Point Functions in the Extended NJL Model
The two-point functions in generalized Nambu--Jona-Lasinio models are
calculated to all orders in momenta and quark masses to leading order in
. The use of Ward identities and the heat-kernel expansion allows for a
large degree of regularization independence. We also show how this approach
works to the same order for three-point functions on the example of the
vector-pseudoscalar-pseudoscalar three-point function. The inclusion of the
chiral anomaly effects at this level is shown by calculating the
pseudoscalar-vector-vector three-point function to the same order. Finally we
comment on how (vector-)meson-dominance comes out in the presence of explicit
chiral symmetry breaking in both the anomalous and the non-anomalous sectors.Comment: Latex, 42 pages, 3 latex figures, 7 postscript figures included,
NORDITA 94/11 N,P. Improvement in the regularization procedure for the PVV
three point functio
Lectures on Chiral Disorder in QCD
I explain the concept that light quarks diffuse in the QCD vacuum following
the spontaneous breakdown of chiral symmetry. I exploit the striking analogy to
disordered electrons in metals, identifying, among others, the universal regime
described by random matrix theory, diffusive regime described by chiral
perturbation theory and the crossover between these two domains.Comment: Lectures given at the Cargese Summer School, August 6-18, 200
Low--Energy Behavior of Two--Point Functions of Quark Currents
We discuss vector, axial-vector, scalar and pseudoscalar two-point functions
at low and intermediate energies. We first review what is known from chiral
perturbation theory, as well as from a heat kernel expansion within the context
of the extended Nambu-Jona-Lasinio (ENJL) model of ref. \cite{12}. In this work
we derive then these two-point functions to all orders in the momenta and to
leading order in . We find an improved high-energy behaviour and a
general way of parametrizing them that shows relations between some of the
two-point functions, which are also valid in the presence of gluonic
interactions. The similarity between the shape of the experimentally known
spectral functions and the ones we derive, is greatly improved with respect to
those predicted by the usual constituent quark like models. We also obtain the
scalar mass independent of the regularization scheme. In the end,
we calculate fully an example of a nonleptonic matrix element in the
ENJL--model, the electromagnetic mass difference and find good
agreement with the measured value.Comment: 37 pages + 6 uuencoded figures, CERN TH 6924/93, CPT-93/P.2917,
NORDITA 93/43-N,
Tensor meson exchange at low energies
We complete the analysis of meson resonance contributions to chiral
low-energy constants of O(p^4) by including all quark-antiquark bound states
with orbital angular momentum less or equal to one. Different tensor meson
Lagrangians used in previous work are shown to produce the same final results
for the low-energy constants once QCD short-distance constraints are properly
implemented. We also discuss the possible relevance of axial-vector mesons with
odd C-parity.Comment: 20 pages, comparison with previous work updated, typos removed,
results unchanged, version to appear in EPJ
Coherent information analysis of quantum channels in simple quantum systems
The coherent information concept is used to analyze a variety of simple
quantum systems. Coherent information was calculated for the information decay
in a two-level atom in the presence of an external resonant field, for the
information exchange between two coupled two-level atoms, and for the
information transfer from a two-level atom to another atom and to a photon
field. The coherent information is shown to be equal to zero for all
full-measurement procedures, but it completely retains its original value for
quantum duplication. Transmission of information from one open subsystem to
another one in the entire closed system is analyzed to learn quantum
information about the forbidden atomic transition via a dipole active
transition of the same atom. It is argued that coherent information can be used
effectively to quantify the information channels in physical systems where
quantum coherence plays an important role.Comment: 24 pages, 7 figs; Final versiob after minor changes, title changed;
to be published in Phys. Rev. A, September 200
Two-point function of strangeness-carrying vector-currents in two-loop Chiral Perturbation Theory
We calculate the correlator between two external vector-currents having the
quantum-numbers of a charged kaon. We give the renormalized expression to two
loops in standard chiral perturbation theory in the isospin limit, which, as a
physical result, is finite and scale-independent. Applications include a low
energy theorem, valid at two loop order, of a flavor breaking combination of
vector current correlators as well as a determination of the phenomenologically
relevant finite -counterterm combination by means of inverse
moment finite energy sum rules. This determination is less sensitive to
isospin-breaking effects than previous attempts.Comment: 24 pages, revtex, 4 figures, 2 tables, revised version, one ref.
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