69 research outputs found
Body composition using bio-impedance analysis in pediatric patients with inflammatory bowel disease. Corcordance with dual energy X-ray absorptiometry and comparison with healthy controls
Introduction: Growth is a central process in paediatrics. Weight and height evaluation are therefore routine exams for every child but in some situation, particularly inflammatory bowel disease (IBD), a wider evaluation of nutritional status needs to be performed. Objectives: To assess the accuracy of bio-impedance analysis (BIA) compared to the gold standard dual energy X-ray absorptiometry (DEXA) in estimating percentage body fat (fat mass; FM) and lean body mass (fat free mass; FFM) in children with inflammatory bowel disease (IBD). To compare FM and FFM levels between patients with IBD and healthy controls. Methods: Twenty-nine healthy controls (12 females; mean age: 12.7 ± 1.9 years) and 21 patients (11 females; 14.3 ± 1.3 years) were recruited from August 2011 to October 2012 at our institution. BIA was performed in all children and DEXA in patients only. Concordance between BIA and DEXA was assessed using Lin's concordance correlation and the Bland-Altman method. Between-group comparisons were made using analysis of variance adjusting for age. Results: BIA-derived FM% showed a good concordance with DEXA-derived values, while BIA-derived FFM% tended to be slightly higher than DEXA-derived values (table). No differences were found between patients and controls regarding body mass index (mean ± SD: 19.3 ± 3.3 vs. 20.1 ± 2.8 kg/m2, respectively; age-adjusted P = 0.08) and FM% (boys: 25.3 ± 10.2 vs. 22.6 ± 7.1%, for patients and controls, respectively; P = 0.20; girls: 28.2 ± 5.7 vs. 26.4 ± 7.7%; P = 0.91). Also, no differences were found regarding FFM% in boys (74.9 ± 10.2 vs. 77.4 ± 7.1%; P = 0.22) and girls (71.8 ± 5.6 vs. 73.5 ± 7.7%; P = 0.85). Conclusion: BIA adequately assesses body composition (FM%) in children with IBD and could advantageously replace DEXA, which is more expensive and less available. No differences in body composition were found between children with IBD and healthy controls
Derivation of Index Theorems by Localization of Path Integrals
We review the derivation of the Atiyah-Singer and Callias index theorems
using the recently developed localization method to calculate exactly the
relevant supersymmetric path integrals. (Talk given at the III International
Conference on Mathematical Physics, String Theory and Quantum Gravity, Alushta,
Ukraine, June 13-24, 1993)Comment: 11 pages in LaTeX, HU-TFT-93-3
Chiral zero-mode for abelian BPS dipoles
We present an exact normalisable zero-energy chiral fermion solution for
abelian BPS dipoles. For a single dipole, this solution is contained within the
high temperature limit of the SU(2) caloron with non-trivial holonomy.Comment: 9 pages, 1 figure (in 2 parts), presented at the workshop on
"Confinement, Topology, and other Non-Perturbative Aspects of QCD", 21-27
Jan. 2002, Stara Lesna, Slovaki
Quantum Fields in Hyperbolic Space-Times with Finite Spatial Volume
The one-loop effective action for a massive self-interacting scalar field is
investigated in -dimensional ultrastatic space-time ,
being a non-compact hyperbolic manifold with finite volume. Making
use of the Selberg trace formula, the -function related to the small
disturbance operator is constructed. For an arbitrary gravitational coupling,
it is found that has a simple pole at . The one-loop effective
action is analysed by means of proper-time regularisations and the one-loop
divergences are explicitly found. It is pointed out that, in this special case,
also -function regularisation requires a divergent counterterm, which
however is not necessary in the free massless conformal invariant coupling
case. Finite temperature effects are studied and the high-temperature expansion
is presented. A possible application to the problem of the divergences of the
entanglement entropy for a free massless scalar field in a Rindler-like
space-time is briefly discussed.Comment: 13 pages, LaTex. The contribution of hyperbolic elements has been
added. Other minor corrections and reference
Quantum corrections to the mass of the supersymmetric vortex
We calculate quantum corrections to the mass of the vortex in N=2
supersymmetric abelian Higgs model in (2+1) dimensions. We put the system in a
box and apply the zeta function regularization. The boundary conditions
inevitably violate a part of the supersymmetries. Remaining supersymmetry is
however enough to ensure isospectrality of relevant operators in bosonic and
fermionic sectors. A non-zero correction to the mass of the vortex comes from
finite renormalization of couplings.Comment: Latex, 18 pp; v2 reference added; v3 minor change
An Index Theorem for Domain Walls in Supersymmetric Gauge Theories
The supersymmetric abelian Higgs model with N scalar fields admits multiple
domain wall solutions. We perform a Callias-type index calculation to determine
the number of zero modes of this soliton. We confirm that the most general
domain wall has 2(N-1) zero modes, which can be interpreted as the positions
and phases of (N-1) constituent domain walls. This implies the existence of
moduli for a D-string interpolating between N D5-branes in IIB string theory.Comment: 9 pages, REVTeX4; v2: reference adde
Nonperturbative Superpotentials and Compactification to Three Dimensions
We consider four-dimensional N=2 supersymmetric gauge theories with gauge
group U(N) on R^3 x S^1, in the presence of a classical superpotential. The
low-energy quantum superpotential is obtained by simply replacing the adjoint
scalar superfield in the classical superpotential by the Lax matrix of the
integrable system that underlies the 4d field theory. We verify in a number of
examples that the vacuum structure obtained in this way matches precisely that
in 4d, although the degrees of freedom that appear are quite distinct. Several
features of 4d field theories, such as the possibility of lifting vacua from
U(N) to U(tN), become particularly simple in this framework. It turns out that
supersymmetric vacua give rise to a reduction of the integrable system which
contains information about the field theory but also about the Dijkgraaf-Vafa
matrix model. The relation between the matrix model and the quantum
superpotential on R^3 x S^1 appears to involve a novel kind of mirror symmetry.Comment: LaTeX, 45 pages, uses AmsMath, minor correction, reference adde
Thermal Fluctuations of Induced Fermion Number
We analyze the phemomenon of induced fermion number at finite temperature. At
finite temperature, the induced fermion number is a thermal expectation
value, and we compute the finite temperature fluctuations, . While the zero temperature induced fermion number is
topological and is a sharp observable, the finite temperature induced fermion
number is generically nontopological, and is not a sharp observable. The
fluctuations are due to the mixing of states inherent in any finite temperature
expectation value. We analyze in detail two different cases in 1+1 dimensional
field theory: fermions in a kink background, and fermions in a chiral sigma
model background. At zero temperature the induced fermion numbers for these two
cases are very similar, but at finite temperature they are very different. The
sigma model case is generic and the induced fermion number is nontopological,
but the kink case is special and the fermion number is topological, even at
finite temperature. There is a simple physical interpretation of all these
results in terms of the spectrum of the fermions in the relevant background,
and many of the results generalize to higher dimensional models.Comment: 17 pgs, 9 figs, RevTex
Renormalized Path Integral for the Two-Dimensional Delta-Function Interaction
A path-integral approach for delta-function potentials is presented.
Particular attention is paid to the two-dimensional case, which illustrates the
realization of a quantum anomaly for a scale invariant problem in quantum
mechanics. Our treatment is based on an infinite summation of perturbation
theory that captures the nonperturbative nature of the delta-function bound
state. The well-known singular character of the two-dimensional delta-function
potential is dealt with by considering the renormalized path integral resulting
from a variety of schemes: dimensional, momentum-cutoff, and real-space
regularization. Moreover, compatibility of the bound-state and scattering
sectors is shown.Comment: 26 pages. The paper was significantly expanded and numerous equations
were added for the sake of clarity; the main results and conclusions are
unchange
Testing Nonperturbative Orbifold Conjecture
We discuss Strassler's hypothesis of matching nonperturbative effects in
orbifold pairs of gauge theories which are perturbatively planar equivalent.
One of the examples considered is the parent N=1 SU(N) supersymmetric
Yang-Mills theory and its nonsupersymmetric orbifold daughter. We apply two
strategies allowing us to study nonperturbative effects: (i) low-energy
theorems; (ii) putting the theory on small-size T^4 or R^3 x S^1 the parent and
daughter theories are weakly coupled and amenable to quasiclassical treatment.
In all cases our consideration yields a mismatch between the parent and
daughter theories. Thus, regretfully, we present evidence against Strassler's
hypothesis.Comment: Latex, 13 pages, 1 eps figur
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